A multiplex or mux, also known as a bouquet, is a grouping of program services as interleaved data packets for broadcast over a network or modulated multiplexed medium, particularly terrestrial broadcasting. The program services are broadcast as part of one transmission and split out at the receiving end.

The conversion from analog to digital television made it possible to transmit more than one video service, in addition to audio and data, within a fixed space previously used to transmit one analog TV service (varying between six and eight megahertz depending on the system used and bandplan). The capacity of a multiplex depends on several factors, including the video resolution and broadcast quality, compression method, bitrate permitted by the transmission standard, and allocated bandwidth; statistical time-division multiplexing is often used to dynamically allocate bandwidth in accordance with the needs of each individual service. Each service in a multiplex has a separate virtual channel (also known as a logical channel number) for identification and tuning. Depending on the country, a multiplex may be controlled by one broadcaster offering multiple subchannels or may feature services from multiple broadcasters with separate licenses.

Multiplexing has made it possible for many new free-to-air television services to be introduced, some of them expressly designed for carriage as additional channels. In the United States, such services are called digital multicast television networks or diginets. The term is also used in an otherwise unrelated sense to refer to additional channels offered by premium pay television services, such as HBO, similar to its meaning with regard to movie theaters.

Depending on the type of transmission system, individual services are either numbered with whole numbers (e.g. 36) or a two-part channel number (e.g. 20.1) consisting of a major and minor channel number.

The digital conversion in countries where broadcasters retained control of their entire multiplex after switchover permitted broadcasters to introduce new supplemental and ancillary services, many of them national in scope. In Australia, Mexico, and the United States, new TV channels were introduced with national coverage.

The licensing of such additional services varies according to national broadcasting regulations. In the United States, a broadcast license covers the full 6 MHz channel and any services broadcast within it. The United Kingdom frequency plan includes three "universal" multiplexes for the national public service broadcasters and three commercial multiplexes broadcast from a total of 80 transmitter sites.

The ISDB-T specification includes 1seg, a mobile media and data broadcasting service utilizing a portion of the spectrum in each multiplex.

The first multichannel broadcast in Australia was ABC Kids, which broadcast from 2001 to 2003; in the succeeding years, the country's commercial broadcasters also launched secondary services to compete against DVDs and online piracy. However, their ability to do so was hampered at first by a ban on adding channels, with a focus on such services as datacasting and high-definition. It was not until 2009 that commercial broadcasters were allowed to add multichannels; in that year, the three major networks all did so, bringing the number of channels they offered from three to eleven.