"Sometimes writers say true things about the overall nature of publicity, promotion, and the publishing industry; but alas, not always." -- Teresa Nielsen Hayden

Teresa Nielsen Hayden (born March 21, 1960) is an American science fiction editor, fanzine writer, essayist, and teacher. She is a consulting editor for Tor Books. She has also worked for Federated Media Publishing where in 2007 she revived the comment section for the blog Boing Boing. Nielsen Hayden has been nominated for Hugo Awards five times.

Born Teresa Nielsen, she grew up in a Mormon household in Mesa, Arizona, but was excommunicated from The Church of Jesus Christ of Latter-day Saints in 1980. In her youth, she served as a page in the Arizona House of Representatives. She appended Hayden to her name upon marrying the former Patrick Hayden in 1979; he also took her name, becoming Patrick Nielsen Hayden. The two of them were active members of science fiction fandom and collaborated on various fanzines, including the Hugo-nominated Izzard.

In 1985, she and her husband were TransAtlantic Fan Fund delegates to Europe for Eastercon. Over the next few years, the Nielsen Haydens published at least three TAFF trip reports. From 1985 to 1989, she served on the editorial board of The Little Magazine, a poetry magazine.

She is a former managing editor and, now, consulting editor at Tor Books. In 1994, a collection of her essays, Making Book (ISBN 0-915368-55-2), was published by NESFA Press. It is now in its third printing. The second printing is the preferred edition.

She is also one of the regular instructors for the writing workshop Viable Paradise.

Outside the science-fiction community, Nielsen Hayden is probably best known for her weblog, Making Light, where she writes about a wide range of subjects such as animal hoarding, publishing scams, astroturfing, and global political events. She is the first recorded Internet editor to practice disemvoweling of the entire text of offensive posts; the term itself was coined in a Making Light post by Arthur Hlavaty. She was the first lead comments moderator at the popular blog Boing Boing when it reopened its comments feature in 2007. In June, 2008, a controversy on Boing Boing concerning the "unpublication" of all articles that mention Sex-Columnist Violet Blue has generated criticism of some of her moderation techniques, including disemvowelment.