This paper presents new rigorous proofs of stability and robustness for the decentralized minimal control synthesis (DMCS) and extended minimal control synthesis (EMCS) algorithms, using the concept of system passivity. The stability result imposes no additional restrictions on the decentralized algorithm compared with the centralized form of the algorithm (Hodgson and Stoten 1996). Thus, previous restrictions on the amplitude of cross-coupling terms between degrees-of-freedom of the controlled plant are removed. The robustness results apply in the cases of plant parameter variations and external disturbances.