In 1948, two complementary Standards on antennas were published by the IRE; these were Definitions of Terms and Methods of Testing. Both were the work of the Technical Committee on Antennas. Subsequently, this committee was renamed the Antennas and Waveguides Committee, and three Standards dealing with waveguides were published during the period from 1953 to 1959. The attention of the committee then returned to antennas, and in 1965 Test Procedure for Antennas (IEEE No. 149) was published. This was a revision of the 1948 Methods of Testing; it also contained a short list of new and revised definitions of terms as well as a discussion of their significance. The following Standard Definitions of Terms for Antennas is a comprehensive revision of the 1948 Definitions of Terms. It also supersedes the definitions contained in the 1965 Test Procedure, although the changes in those definitions are few and relatively minor. As this work reached completion, the Antennas and Waveguides Committee divided into two separate committees, one on antennas and one on waveguides. These are now incorporated into the structures of the IEEE Group on Antennas and Propagation and the IEEE Group on Microwave Theory and Techniques, respectively.