Diazo compounds are among the most important building blocks in organic synthesis. Generally, their photoinitiated, thermal, or transition metal catalyzed decomposition yields the corresponding carbenes or metal carbenoids, which subsequently undergo various transformations. Modern chemistry of diazo compounds is dominated by transition metal catalysis, leaving both catalyzed and non-catalyzed phototransformations of these reagents behind. Recently, photoinitiated reactions of diazo compounds have experienced a revival of interest due to the increased understanding of modern photochemistry. This mini-review covers recently published (year >2000) reports on the reactivity of diazo compounds under light irradiation.