In conclusion we investigated the radical methylation reaction using hypervalent iodine(III) merged with copper photocatalysis. Although redox chemistry by single electron transfer cannot be ruled out completely, we emphasize that triplet-triplet energy transfer is far more likely operational between excited photosensitizer and hypervalent iodine(III) reagent. Quantum yields between 0.5 to 2.1% were obtained for different sensitizers, confirmed by kinetic analysis, and the triplet state energy of PIDA was estimated to be around 58 kcal mol -1 . We could show that methyl acetate formation is a key side reaction under radical control, and this method is comparable with conventional methylation conditions. Various heterocycles and carboxylic acids can be methylated effectively in good to high yields and investigations into more challenging nucleophiles are currently ongoing. The triplet energy transfer reactivity of hypervalent iodine reagents opens new avenues in organic methodology in the future due to the broad availability of I(III) reagents, copper catalysts, and the mild nature of the underlying mechanism.