Four-membered oxygen- and nitrogen-containing heterocycles, such as oxetanes and azetidines, possess unique properties that make them desirable for drug discovery and synthesis applications. However, synthesis of these compounds is challenging, limiting their applicability. While cyclobutanes are commonly synthesized by highly atom-economical light-mediated [2+2] reactions, this powerful methodology remains limited for the synthesis of oxetanes and azetidines via the Paternò-Büchi and aza Paternò-Büchi reactions. Herein we report the development of a visible-light mediated inter- and intramolecular aza Paternò-Buchi reactions, harnessing the triplet state of unique cyclic oximes, specifically 2-isoxazoline-3-carboxylates, as imine equivalents for the synthesis of unique azetidine products. Following energy transfer from an iridium photocatalyst, these cyclic oximes initiate [2+2] reactions with unactivated alkenes, allowing access to a broad range of azetidines with excellent yield. Furthermore, we report the use of oxetanes as versatile synthetic intermediates in new transformations resulting in the formation of functionalized alkenes.