The photo-oxidation of iodide (I−) results in the formation of I−I bonds relevant to solar energy conversion. The making (and breaking) of I−I bonds is specifically important to the operation of high-efficiency dye-sensitized solar cells. In this Perspective, the redox chemistry of iodide in aqueous solution is briefly reviewed, followed by recent photoinduced studies in nonaqueous solution. Analogous to thermal electron-transfer studies, two mechanisms have been identified for photodriven I−I bond formation in solution. With regard to breaking I−I bonds, the photodriven cleavage of I−I bonds has been quantified by the reduction of diiodide (I2•−) and triiodide (I3−). Studies at the solution-semiconductor interface present in dye-sensitized solar cells have also revealed that I−I bonds are formed, and I2•− is a product of iodide oxidation. Rapid disproportionation of I2•− to yield I3− and I− products that are not easily reduced by electrons injected into TiO2 is proposed to be key to the success of the I−...