Assembly of the 34-subunit, 2.5 MDa 26S proteasome is a carefully choreographed intricate process. It starts with formation of a seven-membered alpha-ring that serves as a template for assembly of the complementary beta-ring-forming 'half-proteasomes'. Dimerization results in a latent 20S core particle that can serve further as a platform for 19S regulatory particle attachment and formation of the biologically active 26S proteasome for ubiquitin-dependent proteolysis. Both general and dedicated proteasome assembly chaperones regulate the efficiency and outcome of critical steps in proteasome biogenesis, and in complex association.