The ubiquitin/proteasome pathway is the main non-lysosomal route for intracellular protein degradation in eukaryotes. It is instrumental to various cellular processes, such as cell-cycle progression, transcription and antigen processing. Recent findings also substantiate a pivotal role of the ubiquitin/proteasome pathway in the regulation of apoptosis. Regulatory molecules that are involved in programmed cell death have been identified as substrates of the proteasome. Moreover, key regulators of apoptosis themselves seem to have an active part in the proteolytic inactivation of death executors.