Harry Turtledove collaborated with the prolific Martin H. Greenberg on three anthologies on central SF themes, looking back on the 20th century from the early years of the 21st. Book introductions by Turtledove review the theme and discuss prominent examples of novels. Story introductions are biographical.
Most reprinted authors: Poul Anderson (3), then Gregory Benford, Arthur C. Clarke, Joe Haldeman, Larry Niven, and Turtldove himself (2 each).
 
- 
The Best Military Science Fiction of the 20th Century, (Ballantine Del Rey, 2001)
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- 
The Best Alternate History Stories of the 20th Century, (Ballantine Del Rey, 2001)
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The Best Time Travel Stories of the 20th Century, Harry Turtledove & Martin H. Greenberg, eds. (Ballantine Del Rey, 2005)
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Combined Contents by Author and Title
Poul Anderson
 Among Thieves 
   
(Astounding Jun 1957)
 -- The Best Military Science Fiction of the 20th Century
 Eutopia 
   
(Dangerous Visions, 1967)
 -- The Best Alternate History Stories of the 20th Century
 The Man Who Came Early 
   
(F&SF Jun 1956)
 -- The Best Time Travel Stories of the 20th Century
Greg Bear
 Through Road, No Whither
   
(Far Frontiers, 1985)
 -- The Best Alternate History Stories of the 20th Century
Gregory Benford
 Manassas, Again 
   
(IASFM Oct 1991)
 -- The Best Alternate History Stories of the 20th Century
 To the Storming Gulf 
   
(F&SF Apr 1985)
 -- The Best Military Science Fiction of the 20th Century
Ray Bradbury
 A Sound of Thunder 
   
(Colliers Jun 28 1952)
 -- The Best Time Travel Stories of the 20th Century
Orson Scott Card
 Ender's Game
   
(Analog Aug 1977)
 -- The Best Military Science Fiction of the 20th Century
Jack L. Chalker
 Dance Band on the Titanic 
   
(IASFM Jul/Aug 1978)
 -- The Best Alternate History Stories of the 20th Century
C. J. Cherryh
 The Scapegoat 
   
(Alien Stars, 1985)
 -- The Best Military Science Fiction of the 20th Century
Arthur C. Clarke
 Superiority 
   
(F&SF Aug 1951)
 -- The Best Military Science Fiction of the 20th Century
 Time's Arrow
   
(Science-Fantasy #1 1950)
 -- The Best Time Travel Stories of the 20th Century
Jack Dann
 Timetipping 
   
(Epoch, 1975)
 -- The Best Time Travel Stories of the 20th Century
L. Sprague de Camp
 A Gun for Dinosaur
   
(Galaxy Mar 1956)
 -- The Best Time Travel Stories of the 20th Century
Nicholas A. DiChario
 The Winterberry 
   
(Alternate Kennedys, 1992)
 -- The Best Alternate History Stories of the 20th Century
Philip K. Dick
 Second Variety 
   
(Space Science Fiction May 1953)
 -- The Best Military Science Fiction of the 20th Century
David Drake
 Hangman
   
(Hammer's Slammers, 1979)
 -- The Best Military Science Fiction of the 20th Century
Jack Finney
 I'm Scared
   
(Colliers Sep 15 1951)
 -- The Best Time Travel Stories of the 20th Century
Joe Haldeman
 Anniversary Project 
   
(Analog Oct 1975)
 -- The Best Time Travel Stories of the 20th Century
 Hero
   
(Analog Jun 1972)
 -- The Best Military Science Fiction of the 20th Century
John Kessel
 The Pure Product 
   
(IASFM Mar 1986)
 -- The Best Time Travel Stories of the 20th Century
Nancy Kress
 The Price of Oranges 
   
(IASFM Apr 1989)
 -- The Best Time Travel Stories of the 20th Century
Henry Kuttner
 Time Locker
   
(Astounding Jan 1943)
 -- The Best Time Travel Stories of the 20th Century
R. A. Lafferty
 Rainbird 
   
(Galaxy Dec 1961)
 -- The Best Time Travel Stories of the 20th Century
Ursula K. Le Guin
 Another Story or A Fisherman of the Inland Sea 
   
(A Fisherman of the Inland Sea, 1994)
 -- The Best Time Travel Stories of the 20th Century
Brad Linaweaver
 Moon of Ice 
   
(Amazing Mar 1982)
 -- The Best Alternate History Stories of the 20th Century
George R. R. Martin
 Night of the Vampyres 
   
(Amazing May 1975)
 -- The Best Military Science Fiction of the 20th Century
Richard Matheson
 Death Ship 
   
(Fantastic Story Magazine Mar 1953)
 -- The Best Time Travel Stories of the 20th Century
Anne McCaffrey
 Dragonrider
   
(Analog Dec 1967 (+1))
 -- The Best Military Science Fiction of the 20th Century
Larry Niven
 All the Myriad Ways 
   
(Galaxy Oct 1968)
 -- The Best Alternate History Stories of the 20th Century
 Leviathan!
   
(Playboy Aug 1970)
 -- The Best Time Travel Stories of the 20th Century
Kim Stanley Robinson
 The Lucky Strike 
   
(Universe 14, 1984)
 -- The Best Alternate History Stories of the 20th Century
William Sanders
 The Undiscovered 
   
(Asimov's Mar 1997)
 -- The Best Alternate History Stories of the 20th Century
Charles Sheffield
 Trapalanda 
   
(IASFM Jun 1987)
 -- The Best Time Travel Stories of the 20th Century
Lewis Shiner
 Mozart in Mirrorshades
 (by Bruce Sterling &  LS) 
(Omni Sep 1985)
 -- The Best Alternate History Stories of the 20th Century
Susan M. Shwartz
 Suppose They Gave a Peace...
   
(Alternate Presidents, 1992)
 -- The Best Alternate History Stories of the 20th Century
Robert Silverberg
 Sailing to Byzantium 
   
(IASFM Feb 1985)
 -- The Best Time Travel Stories of the 20th Century
Cordwainer Smith
 The Game of Rat and Dragon 
   
(Galaxy Oct 1955)
 -- The Best Military Science Fiction of the 20th Century
Allen Steele
 The Death of Captain Future
   
(Asimov's Oct 1995)
 -- The Best Alternate History Stories of the 20th Century
Bruce Sterling
 Mozart in Mirrorshades
 (by BS & Lewis Shiner) 
(Omni Sep 1985)
 -- The Best Alternate History Stories of the 20th Century
Theodore Sturgeon
 Yesterday Was Monday 
   
(Unknown Jun 1941)
 -- The Best Time Travel Stories of the 20th Century
Harry Turtledove
 Islands in the Sea 
   
(Alternatives, 1989)
 -- The Best Alternate History Stories of the 20th Century
 The Last Article 
   
(F&SF Jan 1988)
 -- The Best Military Science Fiction of the 20th Century
Walter Jon Williams
 Wolf Time 
   
(IASFM Jan 1987)
 -- The Best Military Science Fiction of the 20th Century
Connie Willis
 Fire Watch 
   
(IASFM Feb 15 1982)
 -- The Best Time Travel Stories of the 20th Century