The Sound Editing category, which has also been known as Best Sound Effects and Best Sound Effects editing, was first introduced in 1963. Prior to 1988, it was only occasionally a competitive category with Special Achievement Oscars going out in some years and no Oscar for Sound Editing at all in others. To be perfectly honest, I've never been entirely sure what the difference between Sound Mixing and Sound Editing are, but I'm guessing that Mixing focuses on the overall sound of a film while Editing focuses specificially on how sound effects are incorporated and crafted.
This year's nominees:
Christopher Boyes, Gwendolyn Yates Whittle, Avatar This is the 1st nomination for Whittle and the 6th nomination for Boyes (for Sound Editing), who has two previous wins for his work on Titanic and Pearl Harbor. Boyes is also nominated as part of the Sound Mixing team.
Paul N.J. Ottosson, The Hurt Locker: This is Ottosson's second nomination for Sound Editing. He is also nominated for Sound Mixing for his work on The Hurt Locker.
Wylie Stateman, Inglorious Basterds: This is the 5th nomination for Stateman.
Mark P. Stoeckinger, Alan Rankin, Star Trek: This is the 2nd nomination for Stoeckinger and the 1st nomination for Rankin.
Michael Silvers, Tom Myers, Up: This is the 5th nomination for Silvers, who has one previous win (for The Incredibles), and the 2nd nomination for Myers. The pair also has a nomination from the BAFTAs.