Understanding and addressing health behavior, health promotion, and illness prevention requires the integration of a wide range of health-related disciplines and research methodologies. These fields and approaches are essential for enabling researchers, educators, practitioners, and policymakers to engage meaningfully with health issues, design effective interventions, and conduct appropriate and context-sensitive research. This chapter sets the stage for the Handbook of Health Disciplines, Research Methodologies and Health Matters in Health Behavior, Health Promotion and Illness Prevention by offering a detailed overview of the disciplines and methodologies that underpin the study and practice of health behavior, health promotion, and illness prevention. By engaging with the material presented in this Handbook, readers will gain a deep and integrated understanding of the multifaceted nature of health behavior, health promotion, and illness prevention. They will become familiar with key theoretical and methodological frameworks that can inform their own research, teaching, and professional practice. This chapter, and the volume as a whole, invites critical reflection, interdisciplinary collaboration, and the application of evidence-informed strategies to enhance the health of individuals and communities across diverse global contexts.