This first-of-its-kind monograph provides a comprehensive overview of the field of quantum biology. Operating from first principles, the core quantum mechanical concepts of quantum biology are advanced to provide the theoretical foundation for this emerging field. Essential topics such as open quantum systems theory, biological electron and proton transfer, vibronic interactions, radical pair dynamics, enzyme photochemistry, ultraweak photon emissions, electrodynamic effects on cellular processes, non-covalent interactions, multi-scale modeling of biomolecular systems, and strong quantum correlations in biological catalysts are woven together through a cohesive interdisciplinary narrative. A comprehensive exploration of quantum effects in living systems is presented in a colloquial style, neatly outlining their long-standing importance in the historical development of quantum theory. Physical Principles of Quantum Biology lays the essential groundwork to enable further developments in physics, chemistry, biology, medicine, and technology. This authoritative treatise brings clarity and insight to the fundamental advances being made in the emerging science of quantum biology.