Methods are established for performance testing, calibration, and use of sodium iodide detector systems for the measurement of gamma-ray emission rates of radionuclides, assay for radioactivity, and the determination of gamma-ray energies. Both energy calibration and efficiency calibration are covered. Three techniques are considered: total spectrum counting, which employs a system that counts all events above a low-energy threshold; single-channel analyzer counting, which employs a system with a counting window that establishes upper and lower energy boundaries; and multichannel analyzer counting, which employs a system utilizing multiple counting windows.