Roger Dean & Hazel Smith 
Improvisation Hypermedia and the Arts since 1945 [PDF ebook] 

First Published in 1997. The authors’ purpose in this book is to dissect developments in improvisation in the arts since 1945, with a particular emphasis on process and technique. The approach is analytical and theoretical but is also relevant to practitioners and their audience. Their key argument is that improvisation has been of great importance and value in the contemporary arts, particularly because of its potential to develop new forms (often by breaking definitions).