I am a big mystery fan.  I have started to read more fantasy and science fiction in an effort to expand my reading pleasure.  I was wondering if there is a book or books that exist that combines both mystery and science fiction or fantasy in them???

I don't know much about fantasy beyond Lord of the Rings and Conan the Barbarian.  As far as sci-fi, Isaac Asimov wrote mysteries, but I'm not sure how much the sci-fi element played a part.  Greg Bear's Slant reads like a mystery, but it's quite heavy on the sci-fi as well as some adult themes that usually keep me from recommending it.  Philip K. Dick novels definitely leave the explaination out until the end, each plot basically being about the main character unraveling their own personal mystery.  I'm sure there have to be whodunit books set in the future or outerspace, but I come from the sci-fi side of this coin.  I think my Mom reads a series of murder mysteries set in the future but I'll have to edit this post to include that info after I get a chance to ask her.  Hope this helps point you in the right direction :)

edit: I noticed your post in one of the other forums and it is the "In Death" series by Nora Roberts writing as J. D. Robb that's set in the future.  My mom's diehard about mystery and she's working on collecting all of the series which has over 20 volumes, nearing 30 by the end of '08.

Dresden Files - combines both mystery and fantasy together. They are written by Jim Butcher

Thank you for your suggestions...I will check to see which ones are available.

The best-known sf/mystery genre blend is The Caves of Steel, by Isaac Asimov.  It's a robot police detective in an sf setting.  There are sequels - The Naked Sun, and The Robots of Dawn. 

Also, depending on the type of mysteries you like, you may find you also like cyberpunk.  Try Pattern Recognition, by William Gibson. 

-Tom Hl.

I agree with JimiJam's assessment of Greg Bear's Queen of Angels and Slant.  But they are more like mysteries for sf fans, than sf for mystery fans, if you know what I mean.

I think lots of sci-fi books are, by their nature, mysteries of the scientific kind, sort-of-like technological CSI. There's often some mysterious force/object/disaster which scientific-minded folks need to puzzle out and prevent/deal with. For example:

  -The 'Academy' series of books by Jack McDevitt (hard-SF, somewhat slow, lots of mystery)

  -The 'Disappeared' novels by Kristine Kathryn Rusch (fast-paced futuristic crime mysteries, less sciency than most)

  -The Uplift novels by David Brin (futuristic adventures with mysterious elements)

Most of these are relatively popular, and only available to the patient wish-lister. Still, being popular means that most libraries will have at least a few.

Tamara Siler Jones has three fantasy books out that combine psuedo-medieval fantasy with forensics. It's an odd combination, but ends up working really well. No dragons and elves quest-type fantasy, but more fantasy with dark magic and ghosts.

You might try Randall Garrett's "Lord D'Arcy" series which is a Victorian setting with magic.  D'Arcy is a royal investigator with his sidekick a sorcerer.  Very Sherlock Holmes in feel. 

There are also quite a lot of mystery and paranormal blends currently out - involving psychics, witches and the like:

Victoria Laurie  Abby Cooper, Psychic Eye and sequels

Shirley Damsgaard's Opehlia and Abby series

Charlaine Harris's Grave series.

Those are more cozy-mystery sort of style, rather than the more graphic settings of Laurell Hamilton and the like. 

The Asimov books that Tom listed.

There are also Richard Morgan's Takeshi Kovacs series about a detective who lives in a  society where everyone's personality is imprinted on a core so if the body gets killed the core can be placed  in a clone body and life continues--handy for the hard boiled detective.

  David Brin's Kiln People is about a privatae eye in a world where technology has advancd to where you can make copies of yourself (out of clay).  The copies can do the grunt wrok, run errands, experience things flesh and blood wouldn't survive.

  Alfred Bester's Demolished Man is a mystery about a man who commits murder and hides it in a world where telepathy exists.

  Larry Niven has a series about Gil "The Arm" Hamilton, a detective who solves crimes and protects society from organ-leggers in a world where you can replace any body part that wears out or gets broken.  Criminals get disassembled for parts but there are still never enough so there is a back market in spare parts.

And a newer addition is The Automatic Detective by Lee Martinez about a robot detective.  Very funny.“Martinez tickles the funny bone in this delightful, fast-paced mishmash of SF and hard-boiled detective story. . . . A smart, rocket-fast read with a clever, twisty plot that comes to a satisfying conclusion.”---Publishers Weekly (starred review) on The Automatic Detective

  The first Takeshi Kovacs book is called Altered Carbon.

I just finished reading Oxygen by John Olson and Randall Ingermanson. It had a sort of sci-fi/mystery feel to it, and I really liked it.

Simon R. Green's Nightside series is a combination of mystery and fantasy, and I'll second the Dresden Files recommendation :)