This book is a comprehensive introduction to the methodological basis of population health research, and a critical assessment of theoretical issues affecting the quality of research on health and behaviour. Research into the many factors that shape human health or illness, has traditionally emphasized experimental design and the statistical effects of specific factors. While due attention is paid to such methods, the contributors emphasize the importance of theory-guided, multi-method approaches for research into the complex forces affecting health, health-related behaviour and the effectiveness of health services. Throughout, the value of analytical models of population health is related to their utility in informing and building theoretical knowledge.