Reductive single electron transfer (SET) to small molecules is a fundamental elementary step that underpins diverse and powerful synthetic transformations. The exquisite chemoselectivity of photoredox catalysis has rendered it an attractive strategy for promoting reductive SET. However, when considering classic photoredox catalyst parameters: (1) E1/2(PC•+/PC*) and (2) E1/2(PC/PC•–), many substrates are expected to remain inert. We hypothesized that new (photo)reductants generated in situ could promote catalysis as well as engage in direct substrate reduction. This would enable the reduction of substrates precluded using conventional photocatalytic systems by their deep reduction potentials. Furthermore, these studies present a roadmap to develop challenging reductive bond cleavage reactions by coupling potent reductants to fragmentation promoters. This talk will demonstrate insight into the mechanism and general principles of photoredox catalysis and illustrate new synthetic applications (SET activation of aryl chlorides, phenols, anilines, and alcohols) of these systems.