Here is the thoroughly revised third edition of the bible of improvisational theater.
Viola Spolin's improvisational techniques changed the very nature and practice of modern theater. The first two editions of "Improvisation for the Theater "sold more than 100,000 copies and inspired actors, directors, teachers, and writers in theater, television, film. These techniques have also influenced the fields of education, mental health, social work, and psychology.
Also available: Spolin's "Theater Game File"
Improvisation for the Theater
Northwestern University Press