This book provides a comprehensive overview to the science of happiness research. It discusses scholarly definitions and measurements, and factors personal, social and cultural that reliably increase happiness throughout the life-span. Anchored in psychology, philosophy, economics and public health, the book distils hundreds of peer-reviewed studies into one lucid, teachable framework. Part I traces the idea from classical eudaimonia to modern positive psychology, then untangles more than thirty related terms well-being, flourishing, thriving, life satisfaction and others into a working map of key distinctions. The discussion shows why happiness remains one of the most diversely interpreted phenomena in the social sciences and why no single definition yet commands unanimous agreement. Part II presents a multilevel map of determinants, starting with personality and health, then progressing to relationships, income, culture, and the built and natural environments. The final chapter in this part evaluates evidence-based interventions, showing how current research can inform realistic, context-sensitive pathways to greater well-being from gratitude practices and mindset trainings to policy levers aimed at housing affordability, neighborhood quality, institutional fairness, and life-course support. Each chapter weighs competing findings, flags methodological caveats and pinpoints areas of empirical convergence. Written for graduate students, researchers and reflective practitioners, this book offers conceptual rigour without sacrificing readability. Readers will finish equipped to design stronger studies, craft data-driven policies and pursue personal well-being grounded in evidence rather than myth.