This book is a classic in terms of understanding systems approach.
Haley gives suggestions to change human problems in the social context they appear (family, school, at work, or the interaction between these).
The first chapter is one of the best guides to interview people with issues that I've ever read.
While it may be dated in some aspects, it still remains as an important source for clinicians and school and health workers, beacause its conceptual framework is easy to adapt to different professions and social organisations.