This chapter is mainly devoted to the photochemistry of carbonyl compounds, although it also contains some photoreactions of other oxygen containing functions, for instance photochemical ring opening of strained cyclic ethers. Due to space limitations and to the broad time coverage (mid 2004 through mid 2007), only those articles containing original experimental results are quoted. In general, reviews and theoretical calculations are not included. The material is organised according to the well-known types of reactions (e.g., Norrish, Paternò-Büchi, photo-Fries, etc.). Within each section, the basic organic photochemical findings are reported first. They are followed by more specific aspects, such as stereoselectivity or applications to the synthesis of natural products or structurally interesting molecules. Special attention is paid to photochemical reactions in heterogeneous and constrained media, including zeolites, polymers or organic crystals. Finally, the mechanistic advances are highlighted, especially when they are based on direct detection of reaction intermediates by means of laser flash photolysis or related time-resolved techniques.