This review provides an overview of proton-coupled electron transfer (PCET), a fundamental process in chemistry and biology. PCET involves the simultaneous transfer of electrons and protons, which is crucial for energy conversion and storage. The review discusses the mechanisms, thermodynamics, and theoretical aspects of PCET, highlighting its importance in biological systems such as photosynthesis and respiration. It covers various reaction pathways, including concerted electron-proton transfer (EPT), multiple site electron-proton transfer (MS-EPT), and hydrogen atom transfer (HAT). The review also addresses the role of pH, solvent effects, and the influence of electronic coupling on PCET processes. It discusses the thermodynamic and kinetic factors that govern PCET, including the impact of proton transfer on reaction rates and the role of proton transfer channels in biological systems. The review emphasizes the significance of PCET in energy conversion, particularly in the context of photosynthesis, where it plays a key role in the storage and release of energy. The review also highlights the importance of understanding PCET in the development of efficient energy conversion technologies and catalytic processes.This review provides an overview of proton-coupled electron transfer (PCET), a fundamental process in chemistry and biology. PCET involves the simultaneous transfer of electrons and protons, which is crucial for energy conversion and storage. The review discusses the mechanisms, thermodynamics, and theoretical aspects of PCET, highlighting its importance in biological systems such as photosynthesis and respiration. It covers various reaction pathways, including concerted electron-proton transfer (EPT), multiple site electron-proton transfer (MS-EPT), and hydrogen atom transfer (HAT). The review also addresses the role of pH, solvent effects, and the influence of electronic coupling on PCET processes. It discusses the thermodynamic and kinetic factors that govern PCET, including the impact of proton transfer on reaction rates and the role of proton transfer channels in biological systems. The review emphasizes the significance of PCET in energy conversion, particularly in the context of photosynthesis, where it plays a key role in the storage and release of energy. The review also highlights the importance of understanding PCET in the development of efficient energy conversion technologies and catalytic processes.