This report summarizes the proceedings of a workshop, co-sponsored by the U.S. Environ-mental Protection Agency (USEPA) and the Swedish Radiation Protection Authority (SSI), held September 11–13, 2001 in Stockholm, Sweden. The invitations to participate in the Workshop were primarily extended to authorities in countries with major nuclear waste programs involving geological disposal and using performance assessment methodology. The main objective of the Workshop was to develop a common understanding among regulators of the role of society and the biosphere in demonstrating compliance with regulations.