Contents:
(Preface by Eric Flint - editor)
The Prisoner
Seller's Market
Top Rung
Symbols
Foghead
The Ghost Fleet
Cargo for Colony 6
Achilles's Heel
Of Enemies and Allies
The Kindly Invasion
Mission of Ignorance
Brains Isn't Everything
The Captive Djinn
The Uninvited Guest
Sabotage
Mind Partner
A Question of Identity
Advance Agent

Original appearances from 1956 to 1995: most from Astounding or Analog, plus Worlds of Tomorrow, Magazine of F&SF, Galaxy. "Of Enemies and Allies" is original to this collection, and 3 of the middle stories have been revised.