The ubiquitin-proteasome system (UPS) is a central regulator of protein turnover and signaling, with E3 ubiquitin ligases conferring substrate specificity and chain-type control. Recent advances have revealed new mechanistic classes of E3 ligases and expanded our understanding of their roles in disease, including cancer, neurodegeneration, and immune dysfunction. These insights have fueled the development of targeted protein degradation strategies that harness the UPS to eliminate disease-associ...