The report is concerned with making recommendations for the specifications of gamma ray sources, which relate to the quantity of radioactive material and the radiation emitted. Primary consideration is given to sources in teletherapy and to a lesser extent those used in industrial radiography and in irradiation units used in industry and research. Space is given to the specification of sources for each type of use. The appendix contains material on "Practical Considerations in the Design of a Low Scattered Cell,""Primary and Scattered Radiation from Typical Sources and Collimators," and "Measurements of Equipment Conversion Ratio." (DS)