A telethon is a fundraising event broadcast on television that lasts many hours or even days, the purpose of which is to raise money for a charitable, political, or other allegedly worthy cause. Correspondingly, the term, a portmanteau, derives from the words "television" and "marathon." The format of a telethon usually consists of performances by singers, musicians, comedians, or other entertainers interspersed with pitches for donations. Typically the program is staged on a set containing volunteer telephone operators, a stage, a tote board that displays the amount of money raised, a band, and a studio audience.

Telethons are held for various organisations around the world. In the United States, telethons are held for groups such as Muscular Dystrophy Associations, the St. Jude Children's Hospital; the Shriners; Chabad; and the Public Broadcasting System. In the United Kingdom, regular telethons are held for charitable groups such as Comic Relief and the BBC's Children in Need.

The most successful annual Telethon per capita in the world is run over 25 hours in Perth, Western Australia, by the Seven Network for the Princess Margaret Children's Hospital, Perth.

The 2004 Asian Tsunami also led to telethons being held in countries such as Canada (CTV) and the United States (NBC).