This account describes work, performed by my research group during the past decade, designed to understand the mechanistic roles of cosolvents and additives in reductions involving samarium(II) iodide (SmI 2 ). Emphasis is placed on studies designed to elucidate the roles of the cosolvent hexamethylphosphoramide (HMPA) and proton donors (water, alcohols, and glycols) in the mechanisms of important bond-forming reactions and reductions initiated by SmI 2 .