The introduction of reactive functionality into feedstock molecules is a well-established strategy for accessing higher-value products from abundant hydrocarbons. To this end, alcohols are ideal targets for synthetic elaboration, 1 supported by an expansive methodological framework that encompasses oxidative, redox-neutral, and reductive transformations. Catalytic methods that generate alcohols directly from alkenes are therefore impactful in chemical synthesis, especially where high chemo-and regioselectivity is achieved. Reductive hydroformylation, a transition metal catalyzed reaction involving the addition of carbon monoxide (CO), and hydrogen (H2) to alkenes, is an atom economical method for the direct synthesis of C1homologated alcohols. The tandem process involves the initial generation of aldehydes and subsequent reduction (Scheme 1A). Following the discovery of Roelen's cobalt hydroformylation catalyst, HCo(CO)4, attempts to improve the performance of the cobalt complexes by addition phosphines (PR3Co(CO)3H; R = alkyl, aryl) modified the product distribution to include C1homologated alcohols arising from a more hydridic Co-H bond. Poor regioselectivity and forcing conditions (>25 atm CO/H2, >180 ºC) motivated the transition to rhodium and ruthenium catalysts that exhibited improved selectivity for alcohol formation from minimally-functional alkenes. While cobalt catalysis has been used commercially for the synthesis homologated alcohols from C8-C15 streams, 1 rhodium has also been used emphasizing the value of regioselectivity in the seminal reaction. 50:1 (l/b). The combination of [Rh(COD)Cl]2 and XantPhos enabled the regiocontrolled synthesis of aldehydes that were reduced in a subsequent, chemoselective hydrogenation step using Shvo's ruthenium catalyst (Scheme 1B). Nozaki and Beller have since reported single-component ruthenium catalysts for the reductive hydroformylation of terminal and internal alkenes (Scheme 1C). 11 For cobalt, a catalytic method that accomplishes highly regioselective reductive hydroformylation has not yet been realized, where progress is likely challenged by the requirement for high pressures and temperatures. The paucity of Earth-abundant transition metal catalysts for the synthesis of alcohols from alkenes inspired the development of a reductive hydroformylation method, targeting synthetically-useful selectivities under mild operating conditions readily accessed in a synthetic laboratory. A catalytic method for selective alcohol synthesis applying the organometallic photochemistry of welldefined cobalt hydrides developed for hydroformylation was envisioned. Irradiation of cobalt hydride precatalysts with visible light is known to promote ligand dissociation and has enabled chemo-and regiodivergent hydroboration and isomerization that complements reactivity under analogous thermal (dark) conditions. Our group recently reported the divergent reactivity of the bis(phosphine)cobalt hydride, (R,R)-( iPr DuPhos)Co(CO)2H (Co-1) under both thermal and photochemical conditions. Hydrogen atom transfer (HAT) reactivity was operative at high temperature, whereas visible-light-irradiation of Co-1 suppressed one-electron chemistry and enabled redox neutral catalysis leading to marked improvement in both rate and scope in hydrogenation. The possibility of a visible-light-driven reductive hydroformylation was explored with Co-1 as the precatalyst, recognizing that photochemical CO dissociation under syngas pressure may enable alkene coordination and subsequent insertion into a relatively hydridic Co-H bond. To achieve the desired selectivity in a tandem process, CO migratory insertion from linear cobalt alkyls would follow the 1,2-insertion of an alkene into a photogenerated, 4-coordinate bis(phosphine)cobalt hydride (Table ). Acyl hydrogenolysis would then have to outcompete isomerization processes that might erode regioselectivity for aldehyde before reduction to alcohol. The observation of aldehyde release upon exposure of the well-defined cobalt acyl complex (R,R)-( iPr DuPhos)Co(CO)2C(O)CH2CH2Ph to 4 atm of H2, suggested that the desired reaction may be accelerated by visible light.