Nebula Awards 21 is an anthology of award-winning science fiction short works edited by George Zebrowski, the second of three successive volumes under his editorship.

The pieces by Card, Silverberg and Blaylock ("[p]erhaps best of all") are singled out for comment, as are the "three critical essays, two of which (by Algis Budrys and Gregory Benford) are stimulating reevaluations of science fiction.

"[2] John G. Cramer in the Los Angeles Times judges the book a "first rate anthology," commenting on the pieces by Kress ("rather mainstream"), Martin ("a very writerly tale") and Silverberg, while noting those by Haldeman, Card, Blaylock and Waldrop as "also excellent."

He criticises the inclusion of the lengthy (40 pages) discussion of science fiction films, however, opining that "[i]f I have any problem ... it is the inappropriateness of the latter piece.

It is regrettable that the editor chose to devote 14% of the anthology to a survey of films, which, in many cases, deserve obscurity."