The NEA's Working Party on Decommissioning and Dismantling (WPPD) Workshop on Safe, Efficient, and Cost-Effective Decommissioning was held in Rome, Italy on 6-10 September 2004. Its purpose was to enable international experts on decommissioning to compare and evaluate respective approaches and experiences in decommissioning nuclear power and fuel cycle facilities and to formulate proposals for future international cooperation in the decommissioning arena. This document contains the proceedings of the workshop.