O-Linked β-N-acetylglucosamine (O-GlcNAc) is a critical post-translational modification (PTM) of thousands of intracellular proteins. Reversible O-GlcNAcylation governs many aspects of cell physiology and is dysregulated in numerous human diseases. Despite this broad pathophysiological significance, major aspects of O-GlcNAc signaling remain poorly understood, including the biochemical mechanisms through which O-GlcNAc transduces information. Recent work from many laboratories, including our own, has revealed that O-GlcNAc, like other intracellular PTMs, can control its substrates' functions by inhibiting or inducing protein-protein interactions. This dynamic regulation of multiprotein complexes exerts diverse downstream signaling effects in a range of processes, cell types, and organisms. Here, we review the literature about O-GlcNAc-regulated protein-protein interactions and suggest important questions for future studies in the field.