Widespread acceptance of the four printings of the first edition of Reference Data for Radio Engineers prompted this larger and improved second edition. Like its predecessor, it is presented by the Federal Telephone and Radio Corporation as an aid in the fields of research, development, production, operation, and education. In it will be found all the material that proved so useful in the first edition along with much additional data—some the result of helpful suggestions from readers, others stemming from rapid advances in the art, and still others now made possible by declassification of many war developments.