First I am curious about how others would define 'hard' science fiction. My take on it is anything that comes more from a science point of view than a fantasy one. Sure some imagination does help to 'suggest' potential new concepts, but turning to wizards and such for changes not currently obtainable just doesn't cut it for me.

Next - what authors/books would those who prefer this type of fiction include in this category? Many of those I like and have read seem to be 'aging' and retiring.

My list includes -

Poul Anderson

Isaac Asimov

Greg Bear

Gregory Benford

Ben Bova

C. J. Cherryh

Arthur C. Clarke

Robert Heinlein (dated science-wise, but fun & interesting read)

James P. Hogan

Nancy Kress

Larry Niven & Jerry Pournelle (together)

Vernor Vinge

More cyberpunk-ish, but good

Alan Dean Foster

Bruce Sterling

William Gibson

Looking forward to replies :) - Katcha

It would be hard for me to specify what Hard SF is, but your definition sounds as good as any.  I would add:

Joe Haldeman - current

Robert L. Forward - recent

James Blish - older

Possibly Michael Crichton should be added as well.  He doesn't immediately come to mind as a hard SF author, but he obviously does an incredible amount of scientific research for his books.

Hard sci-fi is fiction that is scientifically acurate (or what we think is acurate).

My favorite author for the subgenre is Alistair Reynolds; the Revelation Space series, in particular.

Thanks for the references - off to check them out for my future reading pleasure. - Katcha

Some define "hard sf" to be science fiction that is technology-oriented, but I think that is too extreme a definition.  I think "hard sf" refers to science fiction that attempts to be scientifcally accurate.  Here's some recent sf novels I recommend:

Mars Crossing - Geoffry Landis

Evolution - Stephen Baxter

Rainbow's End - Vernor Vinge

Spin - Robert Charles Wilson

Darwin's Radio - Greg Bear

Sunstorm - Arthur Clarke and Stephen Baxter

Forty Signs of Rain - Kim Stanley Robinson

-Tom Hl.

Kim Stanley Robinson's Mars trilogy.  (Red Mars, Green Mars, Blue Mars)

David Brin's Earth

Walter Jon Williams'  Aristoi

Neal Stephenson's The Diamond Age

I've heard good things about Charles Stross, but have only read his Science Fantasy Merchant Princes books so far.

I would add Jack McDevitt to the list.

I would add Greg Egan. Each of his stories is based on an application of theoretical physics or math. But unlike some "hard" scif authors, he doesn't let the science get in the way of the story. Good stuff.

I think originally the term meant stories where the science was the whole point - plot and characters were secondary.  (Which brought about the joke of it being "clunky" fiction... not just becasue it's full of robots and other scientific machines, but it also described the writing style!)  Nowadays, however, I think it applies to any SF where the science is based on actual scientific fact or at least widely accepted theory.  To put it in a pop cultural reference (as I always tend to do)... Star Trek leans toward Hard SF, whereas something like Star Wars is pure space fantasy.

I haven't read a lot of SF recently, I was more into it back in my teenage days.  Since then I've had a tendency toward fantasy.  Really the only current stories I've read are Ben Bova's Grand Tour books.  Others I've read are Isaac Asimov (almost all of it - I was obssessed with his books in high school), Arthur C. Clarke, and some Alan Dean Foster, William Gibson and Poul Anderson.  I'd really like to read a lot of the other authors mentioned here already, particularly Robinson's Mars trilogy, Joe Hadelman and Jack McDevitt.  It's just that the TBR pile doesn't seem to go down faster than I add my current must-read authors!

Some current hard SF authors I've liked (in no particular order):

Iain M. Banks - Culture series

David Louis Edelman - (Jump trilogy, last book not yet published)

Adam Roberts - he's out there

Josh Conviser - Echelon

Karl Schroeder

Edward Lerner - he's co-authored with Larry Niven

Richard Morgan

David Marusek

Neal Asher

Kristine Kathryn Rusch - the Retreival Artist series (character driven stories, but neat technology)

Charles Stross (worth mentioning twice) - Halting State, Iron Sunrise, Singularity Sky, Accelerando

Older SF royalty not mentioned - Hal Clement - hard core SF

I would agree with Tom H. -- my understanding has always been that "hard SF" tried as much as possible to be in line with current scientific understanding, while "soft SF" tending to do a lot of hand waving. For example, a lot of "hard SF" writers make their universes operate at slower than lightspeed, because we currently don't believe that barrier can be broken, but the creators of Star Trek just toss some mumbo-jumbo out about anti-matter to let the characters can travel faster than light.

What I've noticed, though, is that many people also use "hard SF" even more narrowly, only describing novels that deal with the "hard" sciences (physics, primarily, though a bit of biology if it's involving terraforming) and not the "soft" sciences (sociology, or even biology in terms of bio-engineering, or ecology) and so Alastair Reynolds would qualify but Ursula LeGuin and Sheri S. Tepper would not.

Yes, hard SF basically has to follow current scientific laws. You can be sort of flexible with this, but generally it minimizes all of the following: time travel, faster than light travel/communication, implausible aliens (sure, all the aliens in the universe happen to be able to interbreed), etc.

If you cut out the time travel you eliminate H.G.Wells to start with. As far as the science part that is accurate -- I agree up to a point. What is accurate changes, rapidly. I think the scientific part must be key to hard sci fi, but if space travel is ruled out

if it must be attributable to laws of science and physics as we now know them you take away the time warp and faster than light travel and what, pray tell, do you have left? I do think that the existence of dragons, fairies of any sort, or anyone who can practice "magic" is a disqualifier.

That said, I would like to add Sam Delaney and Octavia Butler to the list. And I don't care if his science is dated, and I don't care if he once wrote the best vampire novel of them all, Jack Williamson is on my list for anything. And what do you do with Dan Simmons?

The caveat I forgot to mention is that the science must be accurate at the time. . . of course things can change rapidly and become inaccurate, but as long as the novel was accurate at the time it counts.

However, I still wouldn't say H.G. Wells qualifies as hard sci-fi under that definition, though of course he is a grandfather of the sci-fi genre as a whole. His novels, though they didn't contradict current scientific knowledge at the time, didn't make any particular point of trying to extrapolate from current science; he basically wrote adventure stories with some sort of sci-fi twist. (Which is great, I'm not trying to denigrate him.) The authors usually considered hard sci-fi take a great deal of care to take our current understanding of science and technology and extrapolate from there to make the novels as realistic as a sci-fi novel can be. The science tends to make up a very large part of the novel, which is why if the author really isn't talented as a writer, the books end up extremely boring -- more like idea books than actual novels with plots and unique characters.

And there are plenty of writers that refuse to use faster-than-light travel exceptionally well -- Alastair Reynolds is one, where the fact that interplanetary travel is so slow becomes a major plot point, because people sent for don't arrive (and aren't expected to arrive) for centuries from the time they are sent for.

Again, there are plenty of fantastic authors that simply don't fit the hard sci-fi category that are still fantastic authors. Lois McMaster Bujold's Vorkosigan novels, for instance, certainly aren't hard sci-fi, because they do far too much hand-waving about the science and technology underpinning their universe, but they are absolutely fantastic space opera with deepening characterization across the series that I have found unique in all of science fiction.

I thought the last paragraph the best of your response, Phoenix, and certainly the wisest. I just dug up a book titled Fundamental Disch and  posted it, but only for four or five days to see what happens. Try to put this guy into a category, I double-dog dare you. And Philip Jose Farmer, who came up with for my money the most intriguing scenario of all. It probably isn't hard sci-fi and certainly isn't fantasy. And we certainly would be stupid, not to mention narrow-minded, to denigrate fantasy writers. To understand and appreciate Jordan, the greatest in my book, you need to have read Joseph Campbell, particularly The Hero With A Thousand Faces. And a bit of Jung helps too.