This publication is the proceedings of the fourth in a series of conferences convened by the IAEA on effective nuclear regulatory systems. The conference brought together senior regulators in the areas of nuclear and radiation safety as well as nuclear security from around the world to discuss how to improve regulatory effectiveness to ensure the protection of the public and the environment. The conference built upon the conclusions and deliberations of the past to review issues that are important to the global nuclear regulatory community. These proceedings include the opening addresses, and the session summaries.