A callbook is a directory of radio station call signs. Originally a bound book that resembled a telephone directory, it contains the name and addressees of licensed radio stations in a given jurisdiction (country). Modern Electrics published the first callbook in the United States in 1909. Today, the primary purpose of a callbook is to allow amateur radio operators to send a confirmation post card, called a QSL card to an operator with whom they have communicated via radio. Callbooks have evolved to include on-line databases that are accessible via the Internet to instantly obtain the address of another amateur radio operator and their QSL Managers. The most well known and used on-line QSL databases include QRZ.COM, IK3QAR, HamCall, F6CYV, DXInfo, OZ7C and QSLInfo.
- Gernsback, H (May 1909). First Annual Official Wireless Blue Book of the Wireless Association of America (PDF). New York: Modern Electrics Publication. Retrieved 2010-11-24.
- "QRZ.COM". Retrieved 2010-11-24.
- "Qsl Manager - Qsl Info on-line". Retrieved 2010-11-24.
- "World Wide HamCall Callsign Server". Retrieved 2010-11-24.
- "QSL INFORMATION by F6CYV". Retrieved 2010-11-24.
- "DXInfo, your DX web resource". Retrieved 2010-11-24.
- "QSL Search machine by OZ7C". Retrieved 2010-11-24.
- "QSLInfo". Retrieved 2010-11-24.