Exploring Requirements: Quality Before Design, Donald C. Gause and Gerald M. Weinberg. 1989, Dorset House.
This book is an exploration not just of gathering requirements, including the challenges of ambiguity. The authors describe how to clarify expectations by using functions, attributes, constraints, and preferences. They treat exploration of requirements as a human process, including discussion of how to facilitate different types of effective meetings. My favorite part is the set of context-free questions that apply to many situations. (Reviewed Aug., ’09)