Truth in Comedy
Halpern & Johnson
Meriwether Publishing - 16.95 USD
This book basically describes a long format, called Harold , and doing this the book touches on just a bit of everything. It is by no means theoretical, it is not as complete as Keith Johnstone or Viola Spolin `s books but it is a good starter. They cover a number of games, but not as many as Spolin or Johnstone, and they sort of skirt over these games a bit too shallowly.
Still, the book is a good read, for 2 reasons: it is about the only book covering long format Improv, and the notion about Truthfulness in Improv (or Comedy, as the titles says) is also quite refreshing.
Note added June 2003 - check out Chicago Improv , a more recent book that also describes the Harold as well as other Long Form structures.