Appreciative Inquiry is an increasingly popular technique within the wider family of interventions designed to bring about change through cooperation across a whole system, working with a large group of people. Its distinguishing feature is the emphasis on the positive - what is good about the present and offers potential for the future, what aspirations there are for the future, how do we design such a future and what are the concrete steps to start bringing it about.
This book goes into great detail on the rationale for the approach and the step by step activities required to move through the process. It is a well set-out and thorough guide for practitioners.
For a guide to the range of techniques available and a comparison between them, refer to Napuk and Palmer: The Large Group Facilitator's Manual or Bunker and Alban: Large Group Interventions.