Effects of microheterogeneous environments, made up from surfactant aggregates in aqueous solutions, on photochemical reactions are described as well as effects of photochemical reactions on colloidal surfactant systems. The former effects are employed to direct the regioselectivity and stereoselectivity of photodimerizations and the multiplicity-selectivity of photoisomerizations. The latter effects allow the control of macroscopic properties of surfactant solutions via photoreactions of low concentrated, solubilized compounds. Viscosities may be varied in situ and phase transitions in lyotropic liquid crystalline systems may be switched isothermally by exposing samples to suitable radiation. Methods of studying these effects, their origins and their potential applications are discussed.