This book introduces readers to the field of dyadic health science, offering a theoretical understanding of how two people experience and navigate health and illness together. It provides a detailed overview of how the field has evolved over time, exploring its links to relationship science, psychology, nursing and health-related fields, family science, social work, gerontology, and the science of behaviour change. Chapters examine established and emerging theories, methods, and interventions in dyadic health science, providing numerous state-of-the-art examples of best practices in the field. Combining the expertise of the three authors with insights from 22 scholars, the volume evaluates the current challenges and future directions in the field. By making the theory and methods of dyadic health science accessible, this book provides guidance on building research skills for both seasoned professionals and early-career researchers alike.