Bifunctional degrader molecules, also called proteolysis-targeting chimeras (PROTACs), are a new modality of chemical tools and potential therapeutics to understand and treat human disease. A required PROTAC component is a ligand binding to an E3 ubiquitin ligase, which is then joined to another ligand binding to a protein to be degraded via the ubiquitin–proteasome system. The advent of nonpeptidic small-molecule E3 ligase ligands revolutionized the field and ushered in the design of drug-like PROTACs with potent and selective degradation activity.