Reality television is a genre of television programming which presents purportedly unscripted dramatic or humorous situations, documents actual events, and usually features ordinary people instead of professional actors. Although the genre has existed in some form or another since the early years of television, the term reality television is most commonly used to describe programs of this genre produced since 2000. Documentaries and nonfictional programming such as news and sports shows are usually not classified as reality shows.

Reality television covers a wide range of programming formats, from game or quiz shows which resemble the frantic, often demeaning shows produced in Japan in the 1980s and 1990s (such as Gaki no tsukai), to surveillance- or voyeurism-focused productions such as ''Big Brother.

Such shows frequently portray a modified and highly influenced form of reality, with participants put in exotic locations or abnormal situations, sometimes coached to act in certain ways by off-screen handlers, and with events on screen sometimes manipulated through editing and other post-production techniques.

1940s–1950s

Precedents for television that portrayed people in unscripted situations began in the 1940s. Debuting in 1948, Allen Funt's Candid Camera, (based on his previous 1947 radio show, Candid Microphone), broadcast unsuspecting ordinary people reacting to pranks. It has been called the "granddaddy of the reality TV genre." Debuting in the 1950s, game shows Beat the Clock and Truth or Consequences involved contestants in wacky competitions, stunts, and practical jokes.

In 1948, talent search shows Ted Mack's Original Amateur Hour and Arthur Godfrey's Talent Scouts featured amateur competitors and audience voting. The Miss America Pageant, first broadcast in 1954, was a competition where the winner achieved status as a national celebrity.

The radio series Nightwatch (1954-1955), which tape-recorded the daily activities of Culver City, California police officers, also helped pave the way for reality television. The series You Asked For It (1950-1959), in which viewer requests dictated content, was an antecedent of today's audience-participation reality TV elements, in which viewers cast votes to help determine the course of events.

1960s–1970s

First broadcast in the United Kingdom in 1964, the Granada Television series Seven Up!, broadcast interviews with a dozen ordinary seven-year olds from a broad cross section of society and inquired about their reactions to everyday life. Every seven years, a film documented the life of the same individuals in the intervening years, titled 7 Plus Seven, 21 Up, etc. The series was structured simply as a series of interviews with no element of plot. However, it did have the then-new effect of turning ordinary people into celebrities.