(1) oxidative protein modification through electron transfer to a photocatalyst, (2) protein modification activated by the redox cycle of a photocatalyst, (3) protein modification via 1 O2 generation through energy transfer, and (4) protein modification through the activation of a labeling reagent by energy transfer. Photocatalysis, as a robust strategy for activating small molecules, has emerged at the forefront of organic chemistry, experiencing rapid development throughout the 2010s. In these approaches, metal complexes and organic dyes engage in singleelectron transfer (SET) reactions or energy transfer reactions with substrates, converting visible light into chemical energy. In traditional chemical reactions, the process generally proceeds in a "thermodynamically downhill" direction, making a reaction drive toward an energetically favorable direction through energy release. In contrast, photocatalytic reactions enable the introduction of light energy from an external source, raising the energy level of reactants to facilitate "thermodynamically uphill" reactions, which are typically more challenging to achieve. Recently, an increasing number of studies have focused on protein modification through photocatalysis, reflecting a growing interest in this area. While transformations of biomacromolecules using UV light date back several decades including applications in photoaffinity labeling chemistry, approaches utilizing photocatalysis present the advantage of achieving reaction control with visible light, which is considerably more biocompatible than UV light. Reviews have been published, focusing on various perspectives, such as classification based on structural characteristics of catalysts, the application of photocatalytic chemistry in diverse fields, and photochemistry on a broad range of proteins, including photo-click reactions, nucleic acid modifications, and photo-uncaging. In this section, on the other hand, we will focus specifically on applications of protein modification based on different reaction/catalysis mechanisms.