Proton transfer is a fundamental chemical process that involves the movement of a proton from one protonation site to another. It is ubiquitous in nature and plays a vital role in a variety of chemical and biological processes such as photosynthesis and respiration. Proton transfer is often accompanied by energy transfer. In recent decades, with the ultimate goal of better harnessing energy, many experimental and theoretical efforts have been devoted to understanding the mechanisms of proton transfer and studying proton transfer rates.