The Notch signaling pathway is evolutionarily conserved across metazoan species and plays key roles in many physiological processes. The Notch receptor is activated by two families of canonical ligands (Delta-like and Serrate/Jagged) where both ligands and receptors are single-pass transmembrane proteins usually with large extracellular domains, relative to their intracellular portions. Upon interaction of the core binding regions, presented on opposing cell surfaces, formation of the receptor/ligand complex initiates force-mediated proteolysis, ultimately releasing the transcriptionally-active Notch intracellular domain. This review focuses on structural features of the extracellular receptor/ligand complex, the role of post-translational modifications in tuning this complex, the contribution of the cell membrane to ligand function, and insights from acquired and genetic diseases.