State authorities responsible for safeguards implementation (State Authorities) are essential to the application of International Atomic Energy (IAEA) safeguards in a State. Through administration of the State’s System of Accounting for and Control of Nuclear Material (SSAC), State Authorities provide the critical link between safeguards activities at the facility and national levels and verification activities conducted by the IAEA. The more effectively the State Authority performs its role, the more robust the implementation of safeguards. While effectiveness is difficult to define, it clearly includes at least three aspects: (1) the State Authority’s organizational effectiveness generally, (2) its effectiveness as a regulatory body, and (3) its effectiveness in performing the other functions of SSAC administration. Effectiveness also depends on the individual State’s circumstances, including the size and composition of its nuclear sector, the type of safeguards agreements in force (e.g., Small Quantities Protocol, Additional Protocol), and its population and level of economic development. Further, effectiveness typically grows over time, as the State Authority builds capacity and gains experience. The paper identifies some characteristics of effective State Authorities and suggests several approaches for measuring and cultivating effectiveness. It is intended to provide a starting point for discussion among State Authority management and staff about how well they are doing and how they could do better.