This lecture covers the application of dihydropyridines (DHPs) in photochemistry as radical precursors, including historical and biological contexts, synthesis of DHPs, and their use in photoredox and metallaphotoredox catalysis. It also discusses the oxidative fragmentation of alkyl-substituted DHPs and their role in excited state reactivity. The timeline of DHP usage in biomimetic reduction, photoredox catalysis, and radical coupling reactions is presented, highlighting significant advancements in the field.