The perturbation of chemical and transition metal reactivity with light has long been appreciated by the commu-Figure . A) Conventional cross-coupling approaches using two-electron and single-electron disconnections. B) Conventional C-Heteroatom cross-coupling approaches. C) Impact of photochemistry and electrochemistry on modern catalysis and products accessible through such tactics nity. Seminal work by Marcus, Okada, Fagnoni, Mattay, Tanaka, Fukuzumi, Schuster, and others served to build the foundation upon which the resurgence of photochemical methodologies of the past decade is built. Inspired by the recent work by MacMillan, Doyle, and Molander, we became interested in the exploration of Nicatalyzed decarboxylative cross-coupling with aryl halides enabled by visible-light with an eye towards applications in drug discovery. Following those disclosures, we conducted preliminary mechanistic investigations of the dual-catalyzed reactions. Those efforts led to uncovering the unexpected tolerance of the cross-coupling regime to molecular oxygen. We also studied how different solvents and light wavelengths affect coupling efficiency. We then developed other Ni-based metallaphotoredox cross-coupling methodologies for forging C-C, C-S, C-N, and C-O bonds. We have also contributed to the overall mechanistic understanding of metallaphotoredox cross-couplings. Our mechanistic findings highlight (i) that the photoredox catalyst allows access to Ni(I)-species, which promotes certain cross-couplings, (ii) reductive-elimination of a Ni(II) aryl alky complex is the rate-limiting step in C(sp 2 )-C(sp 3 ) cross-coupling, (iii) Ni(0)-species is not always involved in the cross-coupling reactions, (iv) the energytransfer process plays an essential role in C-heteroatom crosscoupling reactions. With the knowledge that energy transfer processes are involved in metallaphotoredox C-heteroatom cross-coupling reactions, we collaborated with Professor Zachary Hudson and designed organic materials for energy transfer photocatalysis. Although it is outside the scope of this account, we have also developed energy transfer-mediated, inter-, and intramolecular, dearomatizing, and nondearomatizing [2+2] cycloaddition reactions.