The use of evidence in medicine and public health is often contentious. Evidence-Based Medicine (EBM) has led to a new generation of ideas about evidence, and introduced the culture and language of evidence-based practice. Yet what is evidence? remains a key contemporary debate, and the appraisal and application of evidence remain a common source of disagreement and misunderstanding. This text examines how evidence is defined and used by eminent thinkers in both medical and public health fields, that is, by academics and practitioners who teach and influence others. The interviews and field research in this book were conducted at a time of evolution and change (1995 - 2000) when EBM was seriously challenging mainstream thinking. A number of different approaches to evidence are described and explained, and their often complementary relationships revealed. The three-dimensional models of evidence that are presented integrate the once competing perspectives, and provide valuable tools for navigating the new era of evidence-based policy and practice. This book will also become one of the essential texts for anyone involved in teaching about evidence in medicine and public health.