Origins and early life

Koestler's father, Henrik Koestler, was born on 18 August 1869 in the town of Miskolc in northeastern Hungary. According to Koestler's authorized biography, Henrik's father, Leopold Koestler, was a soldier in the Austrian Empire's army, who changed his name to "Lipot" to sound more Hungarian. (According to another biography, Leopold Koestler was a Russian Jew who had settled in northeastern Hungary in 1860, where he married a local woman.) Henrik left school at age 16 due to his parents' strained financial circumstances and took a job as an errand boy with a firm of drapers. Determined to improve his prospects, he taught himself English, German and French, and in the course of a few years obtained promotion to the sales department and eventually became a partner in the firm. A few years later, he set up his own business importing textiles into Hungary.

Arthur's mother, Adele Koestler (née Jeiteles, according to his authorized biography, Zeiteles by another biography, pp. 8–9

In 1898 Henrik Koestler met Adele, married her in 1900, and set up household in Budapest, where on 5 September 1905, Arthur, their only child, was born. The Koestlers were relatively prosperous by local standards and lived in spacious, well-furnished, rented apartments in various predominantly Jewish districts of Budapest, large enough to accommodate a resident cook/housekeeper as well as a foreign governess during Arthur's early years., p. 20

Arthur's primary school education started in a local school at age six. The outbreak of World War I in 1914 deprived Henrik Koestler of his foreign suppliers, and his business collapsed. Facing destitution, the Koestlers gave up their Budapest apartment and moved temporarily to a boarding house in Vienna. From that point, the family never again had a permanent home neither in Budapest nor in Vienna, moving frequently from one boarding house to another., p. 24, 26–27 In 1916 Arthur was entrusted to the care of a small boarding school in Baden, near Vienna., pp. 24–25

When the war ended, the Koestlers returned to Budapest, and in 1918 Arthur witnessed at first hand the political chaos that followed the end of the war: the short-lived Hungarian Bolshevik Revolution of 1919, the temporary occupation of Budapest by the Rumanian Army, and finally the White Terror under the right-wing regime of Admiral Horthy., p. 26

In 1920 the family moved to Vienna once again and in September 1922 Arthur enrolled at the Vienna Polytechnical University to study engineering., pp. 24–25 At the same time he also enrolled in a Zionist duelling student fraternity, one of the many different student societies there at the time.

In the autumn of 1925, a few months before his final exams Arthur, in an "unpremeditated and inexplicable act", burned his Matriculation Book, effectively putting an end to his prospect of graduating from the university. The Matriculation Book contained the records of examinations he had passed, the courses attended and other relevant details and it was irreplaceable; graduating without the book was impossible. In the middle of March 1926, Koestler wrote a long and dishonest letter to his parents, telling them that he was going to Palestine for a year as an assistant engineer in a factory and that on his return home the experience will put him in good stead for finding a well-paid job in Austria and laying the foundations for his future prosperity. On 1 April 1926 he left Vienna for Palestine.

1926-1931 Palestine, Paris, Berlin and Polar flight

Koestler arrived in Palestine in April 1926 and for a few weeks lived in an agricultural collective. However, his application to join the collective, (Kvutzat Heftziba), was rejected by its members. For the next twelve months he supported himself by whatever menial work or commercial enterprise he could find in the cities of Haifa, Tel Aviv and Jerusalem, but for most of the time he was penniless and starving, and frequently had to depend on the kindness of friends and acquaintances for survival. His occasional involvement with the writing or editing of broadsheets and other publications, mostly in German, were all short-lived. In the spring of 1927 he left Palestine briefly, to run the Secretariat of Jabotinsky's Revisionist Party in Berlin. Later that same year, through the intervention of a friend, Koestler obtained the position of Middle East correspondent for the prestigious Berlin-based Ullstein-Verlag group of newspapers. He returned to Jerusalem and for the next two years produced a succession of detailed political essays, as well as some lighter reportage, for his principal employer and for other newspapers. He travelled extensively, interviewed heads of state, kings, presidents and prime ministers and greatly enhanced his reputation as a journalist. But by 1929 Koestler was tired of living in Palestine and in June 1929, while on leave in Berlin, he successfully lobbied at Ullstein for a transfer away from Palestine. In September he was sent to Paris to fill a vacancy in the bureau of the Ullstein News Service. A year later, in 1931, he was called to Berlin and appointed science editor of Vossische Zeitung and science adviser to the entire Ullstein newspaper empire. The same year he was Ullstein's natural choice to represent the paper on board the Graf Zeppelin airship's Polar flight, which carried a team of scientists and the Polar aviator Lincoln Ellsworth to 82 degrees North (thus not to the North Pole) and back. During the flight the airship descended on the sea near Franz Jozef Land and met the Soviet icebreaker "Malygin", which had Umberto Nobile on board, who in 1926 (with Amundsen and Ellsworth) and in 1928 visited the North Pole with his own airships "Norge" and "Italia". Koestler was the only journalist on board and his live wireless broadcasts and subsequent articles and lecture tours throughout Europe brought him further kudos. Soon after that he was appointed foreign editor and assistant editor-in-chief of the mass-circulation Berliner Zeitung am Mittag. Throughout 1931 Koestler had been moving closer to the Communist ideology and on 31 December 1931, he applied for membership of the Communist Party of Germany.

The 1930s

Koestler wrote a book on the Soviet Five-Year Plan but it did not meet with the approval of the Soviet authorities and it was never published. In September 1933 he returned to Paris and for the next two years was active in anti-Fascist movements writing propaganda under the direction of Willy Muenzenberg, the Comintern's chief propaganda director in the West.

In 1935 he married Dorothy Ascher, a fellow Communist activist (they separated amicably in 1937). In 1936, during the Spanish Civil War he undertook a visit to General Franco's headquarters in Seville on behalf the Comintern but using the London daily News Chronicle as cover. He had to escape when recognised and denounced as a Communist by a former German colleague. Back in France he wrote L'Espagne Ensanglantée, which was later incorporated into his book Spanish Testament. In 1937 he returned to Loyalist Spain as a war correspondent of News Chronicle but was captured by the Nationalist rebels. From February until June he was imprisoned under sentence of death. He was eventually exchanged for a 'high value' Nationalist prisoner held by the Loyalists, the wife of one of Franco's ace fighter pilots. He is, to this day, one of the only authors to have been sentenced to death and witnessed death row. This experience is thoroughly revisited in Dialogue with Death.

After his release he returned to France and in order to support himself accepted an offer to author a sex encyclopaedia, which was published to great success under the title The Encyclop?dia of Sexual Knowledge by the joint authors of 'Drs. A. Costler, A. Willy, and Others'. In July 1938, he finished work on his novel The Gladiators. Later that year he resigned from the Communist Party and started work on a new novel that in 1941 was to be published in London with the title Darkness at Noon. That same year, 1938, he became editor of the German weekly paper in Paris Zukunft (The Future) In 1939 he met and formed an attachment to the sculptor Daphne Hardy, who subsequently translated the manuscript of Darkness at Noon from German into English and smuggled it out of France for publication in London.

The war years, 1940-45

After the outbreak of World War II the French authorities detained him for several months in Le Vernet Internment Camp as an 'undesirable alien'. They released him in early 1940 due to strong British pressure. Koestler described the period 1939 to 1940 and his incarceration in Le Vernet in his book Scum of the Earth. Shortly before the German invasion of France, in order to get out of the country, he joined the French Foreign Legion, deserted it in North Africa, and made his way to England.

Arriving in England without an entry permit he was imprisoned pending examination of his case. He was still in prison when his book Darkness at Noon was published in early 1941. Immediately upon release he volunteered for army service and while awaiting his call-up papers and a posting he wrote Scum of the Earth (January-March 1941), which was the first book he wrote in English. For the next twelve months he served in the Pioneer Corps

In March 1942 he was assigned to the Ministry of Information where he worked as a scriptwriter for propaganda broadcasts and films. In his spare time he wrote a novel, Arrival and Departure, and a number of essays, which were subsequently collected and published in The Yogi and the Commissar. One of the essays, titled On Disbelieving Atrocities, (originally published in the New York Times) dealt with the Nazi atrocities being committed against the Jews, as did several of his other articles at the time. Daphne Hardy, who had been doing war work in Oxford, joined him in London in 1943 but they parted company a few months later, although they remained very good friends until Koestler's death. In December 1944 he travelled to Palestine with an accreditation from The Times newspaper. There he had a clandestine meeting with the head of the Irgun underground organisation, Menachem Begin, who was wanted by the British and had a £500 bounty on his head, but Koestler failed to persuade him to abandon militant attacks and accept the prospect of a two-state solution for Palestine after the war. Many years later, Koestler wrote in his memoirs: “When the meeting was over, I realized how naïve I had been to imagine that my arguments would have even the slightest influence.”

He stayed in Palestine until August 1945, collecting material for his next book Thieves in the Night, then returned to England, where the new woman in his life, Mamaine Paget, was waiting for him.

The post-war years

1945-55

January 1949 he and Mamaine moved to a house he bought in France, where he wrote a contribution to The God That Failed and finished work on Promise and Fulfilment. The book received poor reviews both in the U.S. and in England. His other book to come out in 1949 was Insight and Outlook. This too received lukewarm reviews. In July he commenced work on the first volume of his autobiography, Arrow in the Blue. In the same month a new part-time secretary started working for him, Cynthia Jefferies, who eventually would become his third wife. In the autumn he started work on The Age of Longing on which he continued to work until the summer of 1950.

During the summer he had reached agreement with his first wife, Dorothy, for an amicable divorce and their marriage was annulled on 15 December 1949.. This cleared the way for his marriage to Mamaine Paget, which took place on 15 April 1950 at the British Consulate in Paris.In June he delivered a major speech at the CIA-front Congress for Cultural Freedom held in Berlin. In the autumn he went to the United States on a lecture tour and was at the same time actively lobbying for permanent resident status in the U.S. for himself.At the end of October, entirely on impulse, he bought a small island with a house on it on the Delaware River in Pennsylvania with the intention of living there at least for part of each year.

For two years, 1945—47, Koestler worked on Insight and Outlook.In March 1948 he went on a literary and political lecture tour in the United States. When soon after his return from the U.S. war broke out between the newly declared State of Israel and the neighbouring Arab states, he travelled to Israel with accreditations from several newspapers, American, British and French. Mamaine Paget went with him. They arrived in Israel on 4 June and stayed there until October. Later that year they decided to leave England for a while and move to France. News that his long-pending application for British nationality had been granted reached him in France in late December. Early in the new year (1949) he returned to London to swear the oath of allegiance to the British Crown.In January 1949 he and Mamaine moved to a house he bought in France. That same year his book Insight and Outlook was published. He commenced work on his autobiography Arrow in the Blue, assisted by his new part-time secretary, Cynthia Jefferies.

In January 1951 the dramatized version of Darkness at Noon, by Sidney Kingsley, opened in New York. Critics loved the play and it won the New York Drama Critics' Award. Koestler donated all royalties from the play to a fund he set up for helping struggling authors, “Fund for Intellectual Freedom" (FIF)In 1951 the last of his political works, The Age of Longing, was published in which he examined the political landscape of post-war Europe and the problems facing Europe.

In August 1952 his oft-troubled marriage to Mamaine collapsed. They separated but remained very close right up to her sudden and unexpected death in June 1954. The book Mamaine Koestler's Letters 1945-51, edited by Mamaine's twin sister Celia Goodman, gives useful insight into their lives together over those years. After their separation he abandoned earlier plans for living overseas and decided to make his permanent home in England. In May 1953 he bought a three-storey Georgian town house on Montpelier Square in London and sold his houses in France as well as the one in the United States.The first two volumes of his autobiography, Arrow in the Blue, which covers his life up to December 1931 when he joined the German Communist Party, and The Invisible Writing, which covers the years 1932 to 1940, were published in 1952 and 1954 respectively. A collection of essays, The Trail of the Dinosaur and Other Essays, largely on the perils facing civilization, was published in 1955.On 13 April 1955, Janine Graetz, with whom Koestler had an on-off relationship over a period of years in the 1950s, gave birth to a daughter fathered by him. Koestler had virtually no contact with his daughter throughout his life in spite of repeated attempts by Janine to persuade him to meet Cristina and take some interest in her.

Koestler's main polemic during 1955 was his campaign for the abolition of capital punishment and hanging. In July he started work on Reflections on Hanging. Later that same month his former secretary, Cynthia Jefferies, arrived from New York, where she was living at the time, for a few weeks holiday and she was pleased to resume former relations with him, both professional and private. When her extended stay in London was over she returned to New York. In early November, Koestler cabled Jefferies asking her to come back to London for six months to resume secretarial work for him. Jefferies was delighted to oblige. She wound up her affairs in New York and by the end of the month was back in London working for him and with him at the house on Montpelier Square — and she stayed with him for the rest of her life, and his.

1956-75

Although Koestler resumed work on Kepler's biography in 1955 it was not published until 1959, and in the interim it acquired the title The Sleepwalkers. The emphasis of the book changed to 'A history of Man's Changing Vision of the Universe', which became also the book's subtitle. Copernicus and Galileo were added to Kepler as the major subjects of the book. There was plenty to distract Koestler from work. Early in the year it was Jefferies unintended pregnancy and arrangements for an illegal abortion. In October it was the Hungarian uprising and for the next two months he was busy organising anti-Soviet meetings and protests.

In June 1957 Koestler gave a lecture at a symposium in Alpbach, Austria, and fell in love with the village; bought land there, had a house built and for the next twelve years used it as a place for summer vacations and for organising symposia.

In May 1958 he had a hernia operation. In December he left for the East - India and Japan - and was away until the spring of 1959. The resulting book was The Lotus and the Robot.

In the spring of 1960, on his way back from a conference in San Francisco, he interrupted his journey at the University of Michigan, Ann Arbor, where some experimental research was going on with hallucinogens. He tried psilocybin but had a 'bad trip'. Later, when he arrived at Harvard to see Timothy Leary he partook in further experiments with drugs but wasn't enthusiastic about that trip either.In November 1960 he was elected to a Fellowship of The Royal Society of Literature.

The year 1962 was notable for the debate about whether Britain should join the European Common Market. Koestler was strongly in favour of joining and he was greatly disappointed when, in January 1963, Britain's application to join was rejected.

1963 was made notable by Willy Brandt's courtesy call on Koestler in Alpbach. Brandt was Mayor of Berlin at the time. Koestler's book The Act of Creation came out in May 1964. In November he undertook a lecture tour of various universities in California.

The main event of 1965 was his marriage in New York, on 8 January, to Cynthia Jefferies. They then proceeded to California, where, at the Center for Advanced Study in the Behavioral Sciences at Stanford, he participated in a series of seminars.

Koestler spent most of 1966 and the early months of 1967 working on The Ghost in the Machine. In his article Return Trip to Nirvana, published in 1967 in the Sunday Telegraph, Koestler wrote about the drug culture and his own experiences with hallucinogens. The article also challenged the defence of drugs in Aldous Huxley's The Doors of Perception.

In April 1968, Koestler was awarded the prestigious and valuable Sonning Prize “For outstanding contribution to European culture”. The Ghost in the Machine was published in August of same year and in the autumn he received an honorary doctorate from Queen's University, Kingston, Ontario. In the later part of November the Koestlers flew to Australia for a number of television appearances and press interviews, but the experience was not a happy one for him.

At the end of the decade, Koestler was elated to learn that the House of Lords had finally gave their consent to the abolition of hanging for which he had been campaigning for many years.

The first half of the 1970s saw the publication of four more of his books: The Case of the Midwife Toad (1971), The Roots of Coincidence and The Call Girls (both in 1972), and Essays 1968-1973 (1974).

In the New Year Honours List for 1972, he was made a Commander of the Order of the British Empire (CBE).

Final years, 1976-83

Early in 1976 Koestler was diagnosed with Parkinson's disease. The trembling of his hand made writing progressively more difficult. He cut back on overseas trips and spent the summer months at the farmhouse in Denston, Suffolk, which he had bought in 1971. That same year saw the publication of The Thirteenth Tribe.

In 1978 he published A Summing Up. Two years later, in 1980, he was diagnosed also with chronic lymphocytic leukaemia. Walking and writing became an effort and Koestler's physical condition visibly deteriorated but he kept on working. His book Bricks to Babel was published that year. His final book, Kaleidoscope: Essays from Drinkers of Infinity and Essays 1968-1973 and some later pieces and stories was published the following year, 1981.

During the final years of his life he established the KIB Society (with Brian Inglis and Tony Bloomfield), to sponsor research 'outside the scientific orthodoxies' (which, after his death, was renamed The Koestler Foundation), and in his capacity as Vice President of the Voluntary Euthanasia Society, later renamed EXIT, he wrote a powerful pamphlet on suicide, outlining the case both for and against, with a section dealing specifically with how best to do it.

Koestler and Cynthia ended their own lives on the evening of 1 March 1983.

Koestler had stated more than once that he was not afraid of being dead but was afraid of the process of dying. He did not wish to suffer the indignity of losing control over his body or mind. His suicide was not unexpected among close friends. Shortly before his suicide his doctor had discovered a swelling in the groin which indicated a metastasis of the cancer. He and his wife killed themselves on 1 March 1983 with an overdose of barbiturates (Tuinal), taken with alcohol. Their bodies were discovered on the morning of 3 March, by which time they had been dead for thirty-six hours.

Koestler's suicide note:

To whom it may concern.

The purpose of this note is to make it unmistakably clear that I intend to commit suicide by taking an overdose of drugs without the knowledge or aid of any other person. The drugs have been legally obtained and hoarded over a considerable period.

Trying to commit suicide is a gamble the outcome of which will be known to the gambler only if the attempt fails, but not if it succeeds. Should this attempt fail and I survive it in a physically or mentally impaired state, in which I can no longer control what is done to me, or communicate my wishes, I hereby request that I be allowed to die in my own home and not be resuscitated or kept alive by artificial means. I further request that my wife, or a physician, or any friend present, should invoke habeas corpus against any attempt to remove me forcibly from my house to hospital.My reasons for deciding to put an end to my life are simple and compelling: Parkinson's Disease and the slow-killing variety of leukaemia (CCI). I kept the latter a secret even from intimate friends to save them distress. After a more or less steady physical decline over the last years, the process has now reached an acute state which added complications which make it advisable to seek self-deliverance now, before I become incapable of making the necessary arrangements.I wish my friends to know that I am leaving their company in a peaceful frame of mind, with some timid hopes for a de-personalised after-life beyond due confines of space, time and matter and beyond the limits of our comprehension. This 'oceanic feeling' has often sustained me at difficult moments, and does so now, while I am writing this.What makes it nevertheless hard to take this final step is the reflection of the pain it is bound to inflict on my surviving friends, above all my wife Cynthia. It is to her that I owe the relative peace and happiness that I enjoyed in the last period of my life — and never before.

The above note was dated June 1982. Below it appeared the following:

Since the above was written in June 1982, my wife decided that after thirty-four years of working together she could not face life after my death.

Further down the page appeared Cynthia's own farewell note:

I fear both death and the act of dying that lies ahead of us. I should have liked to finish my account of working for Arthur — a story which began when our paths happened to cross in 1949. However, I cannot live without Arthur, despite certain inner resources.Double suicide has never appealed to me, but now Arthur's incurable diseases have reached a stage where there is nothing else to do.

The funeral was held at the Mortlake Crematorium in South London on 11 March.

The first controversy arose about why he allowed or consented to his wife's simultaneous suicide. She was only fifty-five years old and believed to be in good health. In a typewritten addition to her husband's suicide note Cynthia Koestler wrote that she could not live without her husband. Reportedly, few of their friends were surprised by this admission, apparently perceiving that Cynthia lived her life through her husband's and that she had no 'life of her own'. Her total and absolute devotion to Koestler can be seen clearly in her partially completed memoirs. In addition, had she survived her husband's suicide, she might have faced criminal charges for assisting him with the suicide.

This said, according to a profile of Koestler by Peter Kurth:

All their friends were troubled by what Julian Barnes calls "the unmentionable, half-spoken question" of Koestler's responsibility for Cynthia's actions.

"Did he bully her into it?" asks Barnes. And "if he didn't bully her into it, why didn't he bully her out of it?" Because, with hindsight, the evidence that Cynthia's life had been ebbing with her husband's was all too apparent.

The second controversy was occasioned by the terms of his Will. With the exception of some minor bequests Koestler left the residue of his estate, about £1 million, to promote research into the paranormal through the founding of a Chair in Parapsychology at a university in Britain. The Trustees of the Estate had great difficulty finding a university willing to establish such a Chair. Oxford, Cambridge, King's College London and University College London, were approached and all refused. Eventually, the Trustees reached agreement with Edinburgh University to set up a chair in accordance with Koestler's request.

Controversial personal life

Koestler's relations with women have been a source of controversy. In 1998, a biography of Koestler by David Cesarani alleged that Koestler had been a serial rapist and that the British writer Jill Craigie had been one of his victims in 1951. Craigie confirmed the allegations.In his biography Koestler: The Indispensable Intellectual, Michael Scammell countered that Craigie was the only woman to go on record that she had been raped by Koestler, and had only revealed this in public 50 years after the alleged incident.

Scammell admits that Koestler could certainly be rough and sexually aggressive, and others (including Cesarani) claim that Koestler had misogynistic tendencies, reportedly engaging in endless seductions and generally treating the women in his life badly. As argued by Geoffrey Wheatcroft in a review of Cesarani's biography, philandering on this scale is neurotic: a man driven to copulate with as many women as possible not only has difficulty establishing happy relations with women, or regarding them as equals, but does not actually like women.

Darkness at Noon was one of the most influential anti-Soviet books ever written. Its influence in Europe on Communists and sympathisers and, indirectly, on the outcomes of elected governments, was substantial. Ultimately, a writer's legacy is the body of his writing. Koestler wrote several major novels, two volumes of autobiographical works, two volumes of reportage, a major work on the history of science, several volumes of essays and a considerable body of other writing and articles on subjects as varied as genetics, euthanasia, Eastern mysticism, neurology, chess, evolution, psychology, the paranormal and more.

Politics and causes

Koestler embraced a multitude of political as well as non-political issues. Zionism, Communism, anti-Communism, voluntary euthanasia, abolition of capital punishment, particularly hanging, and the abolition of quarantining of dogs being re-imported into the United Kingdom are examples.

Paranormal and scientific interests

During the last 30 years of his life, Koestler wrote extensively on science and scientific practice. A case in point is his 1971 book The Case of the Midwife Toad about the biologist Paul Kammerer, who claimed to find experimental support for Lamarckian inheritance. Mysticism and a fascination with the paranormal also imbued much of his later work.

In The Roots of Coincidence he took an overview of the scientific research around telepathy and psychokinesis and compared it with the advances in quantum physics at that time. It mentions yet another line of unconventional research by Paul Kammerer, the theory of coincidence or synchronicity. He also presents critically the related writings of Carl Jung. More controversial were Koestler's levitation and telepathy studies and experiments.

Hallucinogens

In Return Trip to Nirvana, published in the Sunday Telegraph in 1967, Koestler wrote about the drug culture and his own experiences with hallucinogens. The article also challenged the defence of drugs in Aldous Huxley's The Doors of Perception.

Judaism

Koestler was a secular Jew. In an interview published in the London Jewish Chronicle in 1950 he argued that Jews should either migrate to Israel or assimilate completely into their local cultures.

In The Thirteenth Tribe (1976), he advanced the controversial thesis that Ashkenazi Jews are not descended from the Israelites of antiquity, but from the Khazars, a Turkic people in the Caucasus who converted to Judaism in the 8th century and were later forced westward into present-day Russia, Ukraine and Poland. Koestler argued that by proving Ashkenazi Jews to have no connection with the biblical Jews, European anti-Semitism would lose all basis.

The book received numerous attacks but became immensely popular, and many scholars have expanded upon his thesis, including Israeli historian Shlomo Sand.

Koestler's mother tongue was Hungarian. However, at home, the family spoke mostly German. Thus from early life he was fluent in both languages. It is likely that he picked up some Yiddish too, through contact with his grandfather. By the time of his teens he was fluent in Hungarian, German, French and English.

During his years in Palestine he became sufficiently fluent in Hebrew to write stories in that language and during his years in the Soviet Union, (1932—33), although he arrived there with a vocabulary of only 1000 words of Russian, and no grammar, he picked up enough colloquial Russian to be able to speak the language.

The Gladiators was the first novel that Koestler wrote and the only one written in Hungarian. All his other works up to 1940 were written in German. After 1940 he wrote only in English. (L'Espagne ensanglantée was translated into French from German.)

Fiction

• 1939. The Gladiators. A novel on the revolt of Spartacus.
• 1940. Darkness at Noon.
• 1943. Arrival and Departure, novel.
• 1946. Thieves in the Night.
• 1951. The Age of Longing.
• 1972. The Call Girls: A Tragicomedy with a Prologue and Epilogue. A novel about scholars making a living on the international seminar-conference circuit.

Drama

• 1945. Twilight Bar.

Autobiography

• 1937. Spanish Testament.
• 1941. Scum of the Earth.
• 1942. Dialogue with Death.
• 1952. The First Volume Of An Autobiography, 1905-31, 2005 reprint, ISBN 0-09-949067-6
• 1954. The Second Volume Of An Autobiography, 1932-40, 1984 reprint, ISBN 0-8128-6218-X
• 1984. Stranger on the Square co-written with Cynthia Koestler, published posthumously, edited and with an Introduction and Epilogue by Harold Harris, Hutchinson, London 1984, ISBN 0-09-154330-4.

NB The books The Lotus and the Robot, The God that Failed, and , as well as his numerous essays, all may contain further autobiographical information.

Other non-fiction

• 1934. . About Koestler's travels in the USSR. In his The Invisible Writing, Koestler calls the book Red Days and White Nights, or, more usually, Red Days. Of the five foreign language editions ? Russian, German, Ukrainian, Georgian, Armenian ? which were intended, only the German version was eventually published, "thoroughly expurgated", in Kharkov, Ukrainian S.S.R., and the work is therefore very rare.
• 1937. L'Espagne ensanglantée.
• 1941 Scum of the Earth. Account of his life in France before and after the outbreak of World War Two, with a detailed account of his internment at Le Vernet, the French concentration camp for undesirable aliens.
• 1942 (summer) Le yogi et le commissaire.
• 1945. The Yogi and the Commissar and other essays.
• 1949. The Challenge of our Time.
• 1949. Promise and Fulfilment: Palestine 1917-1949.
• 1949. Insight and Outlook.
• 1955. The Trail of the Dinosaur and other essays.
• 1956. Reflections on Hanging.
• 1959. The Sleepwalkers: A History of Man's Changing Vision of the Universe. ISBN 0-14-019246-8   An account of changing scientific paradigms.
• 1960. The Watershed: A Biography of Johannes Kepler. (excerpted from The Sleepwalkers.) ISBN 0-385-09576-7
• 1960. The Lotus and the Robot, ISBN 0-09-059891-1. Koestler's journey to India and Japan, and his assessment of East and West.
• 1961. Control of the Mind.
• 1961. Hanged by the Neck. Reuses some material from Reflections on Hanging.
• 1963. Suicide of a Nation.
• 1964. The Act of Creation.
• 1967. The Ghost in the Machine. Penguin reprint 1990: ISBN 0-14-019192-5.
• 1968. Drinkers of Infinity: Essays 1955-1967.
• 1970. The Age of Longing, ISBN 0-09-104520-7.
• 1971. The Case of the Midwife Toad, ISBN 0-394-71823-2. An account of Paul Kammerer's research on Lamarckian evolution and what he called "serial coincidences".
• 1972. The Roots of Coincidence, ISBN 0-394-71934-4. Sequel to The Case of the Midwife Toad.
• 1973. The Lion and the Ostrich.
• 1974. Essays 1968-1973, ISBN 0-09-119400-8.
• 1976. The Thirteenth Tribe: The Khazar Empire and Its Heritage, ISBN 0-394-40284-7.
• 1976. Astride the Two Cultures: Arthur Koestler at 70, ISBN 0-394-40063-1.
• 1977. Twentieth Century Views: A Collection of Critical Essays, ISBN 0-13-049213-2.
• 1978. A Summing Up, ISBN 0-394-50052-0. Sequel to The Ghost in the Machine
• 1980. Bricks to Babel. Random House, ISBN 0-394-51897-7. This 1980 anthology of passages from many of his books, described as "A selection from 50 years of his writings, chosen and with new commentary by the author", is a comprehensive introduction to Koestler's writing and thought.
• 1981. Kaleidoscope. Essays from Drinkers of Infinity and The Heel of Achilles, plus later pieces and stories.

Writings as a contributor

• The Encyclop?dia of Sexual Knowledge (1934) (In his autobiography The Invisible Writing, Koestler uses the ligature ? in the spelling of the word "Encyclopaedia".)
• Foreign Correspondent (1940) uncredited contributor to Alfred Hitchcock film produced by Walter Wanger

• The God That Failed (1950) (collection of testimonies by ex-Communists)
• Attila, the Poet (1954) (Encounter ; ; 1954.2 (5)). On loan at the UCL library of the School of Slavonic & Eastern European Studies.
• UCL library online
• Beyond Reductionism: The Alpbach Symposium. New Perspectives in the Life Sciences (co-editor with J.R. Smythies, 1969), ISBN 0-8070-1535-0
• The Challenge of Chance: A Mass Experiment in Telepathy and Its Unexpected Outcome (1973)
• The Concept of Creativity in Science and Art (1976)
• Life After Death, (co-editor, 1976)
• Humour and Wit. I: Encyclopædia Britannica. 15th ed. vol. 9.(1983)
• humour - Encyclopædia Britannica (by Arthur Koestler)

• Atkins, J., 1956. Arthur Koestler.
• Buckard, Christian G., 2004. Arthur Koestler: Ein extremes Leben 1905-1983. ISBN 3-406-52177-0.
• Cesarani, David, 1998. Arthur Koestler: The Homeless Mind. ISBN 0-684-86720-6.
• Hamilton, Iain, 1982. Koestler: A Biography. ISBN 0-02-547660-2.
• Koestler, Mamaine, 1985. Mamaine Koestler's Letters 1945-51. ISBN 0-297-78531-1 or ISBN 0-312-49029-1.
• Levene, M., 1984. Arthur Koestler. ISBN 0-8044-6412-X
• Mikes, George, 1983. The Story of a Friendship. ISBN 0-233-97612-4.
• Pearson, S. A., 1978. Arthur Koestler. ISBN 0-8057-6699-5.

NB Langston Hughes's autobiography also documents their meeting in Turkestan during the Soviet era.