Video on Demand (VOD) or Audio and Video on Demand (AVOD) are systems which allow users to select and watch/listen to video or audio content on demand. IPTV technology is often used to bring video on demand to televisions and personal computers.

Television VOD systems either stream content through a set-top box, a computer or other device, allowing viewing in real time, or download it to a device such as a computer, digital video recorder (also called a personal video recorder) or portable media player for viewing at any time. The majority of cable- and telco-based television providers offer both VOD streaming, including pay-per-view and free content, whereby a user buys or selects a movie or television program and it begins to play on the television set almost instantaneously, or downloading to a DVR rented from the provider, or downloaded onto a pc, for viewing in the future. Internet television, using the Internet, is an increasingly popular form of video on demand.

Some airlines offer AVOD as in-flight entertainment to passengers through individually controlled video screens embedded in seatbacks or armrests or offered via portable media players. Airline AVOD systems offer passengers the opportunity to select specific stored video or audio content and play it on demand including pause, fast forward, and rewind.

On-demand may refer to:

Vinton Gray "Vint" Cerf (/ˈsɜrf/; born June 23, 1943) is an American computer scientist, who is recognized as one of "the fathers of the Internet", sharing this title with American computer scientist Bob Kahn. His contributions have been acknowledged and lauded, repeatedly, with honorary degrees and awards that include the National Medal of Technology, the Turing Award, the Presidential Medal of Freedom, and membership in the National Academy of Engineering.

In the early days, Cerf was a program manager for the United States Department of Defense Advanced Research Projects Agency (DARPA) funding various groups to develop TCP/IP technology. When the Internet began to transition to a commercial opportunity during the late 1980s,^{[citation needed]} Cerf moved to MCI where he was instrumental in the development of the first commercial email system (MCI Mail) connected to the Internet.

Vinton Cerf was instrumental in the funding and formation of ICANN from the start. Cerf waited in the wings for a year before he stepped forward to join the ICANN Board. Eventually he became the Chairman of ICANN. Cerf was elected as the president of the Association for Computing Machinery in May 2012.