Summer Replacement Series

In the United States, most television shows from the late 1940s and early 1950s were performed live, and in many cases they were never recorded, necessitating something to fill their time on the air whenever there was a significant break in the production schedule. Before the invention of kinescope recording made it possible for Groucho Marx to suggest rebroadcasting the best episodes of You Bet Your Life during the program's summer hiatus, networks would create entire an new series to run in the place of an established show. Most of these shows were intended as short-term placeholders, but some managed to gain enough popularity to become regular, full-fledged series in their own rights. Others returned in the summer year after year, essentially sharing their timeslot with their counterparts.

In some cases, a collection of unsold Pilots would fill a timeslot during the summer instead of a series proper, often presented as an Anthology series.

The practice dates back to the days of radio, even though sound recording technology existed early enough to make radio reruns practical. It continued, although substantially diminished in its frequency, through the 1960s to this day on television, and has even made an appearance on the Web, with RWBY Chibi acting as a Summer Replacement Series for RWBY starting in 2016.

Differs from a Midseason Replacement, in that the latter is a complete replacement for a series that has been Cancelled. In some ways the polar opposite of the No Hoper Repeat, as the replacement series was intended to hold the audience and its ratings through the summer, until the "primary" program returned in the fall.

Live-Action TV

 * The Dean Martin Summer Show, which ran on NBC during the summers of 1966-68. Unusual in that it was a replacement series for Dean Martin's regular fall series, created because NBC wanted to keep the ratings Martin generated through the rest of the year.  Also unusual in that Martin didn't bother hosting his own show -- the first season was actually hosted by Dan Rowan and Dick Martin, which led directly to them getting their title gig on Rowan and Martin's Laugh-In.
 * Hee Haw originated in 1969 as a summer replacement for The Smothers Brothers Comedy Hour.
 * The Johnny Cash Show (1969-1971), on ABC.
 * As noted above, averted during the 1950s by You Bet Your Life, which has been cited as the first program to Rerun episodes (originally its "Best of" from the season) during its summer break rather than finance a replacement series. Later in his life, Groucho Marx often took a perverse delight in claiming to have invented the television rerun.
 * Vacation Playhouse, a 1963-67 CBS anthology series which showed nothing but unsold Pilots.
 * The Lucy-Desi Comedy Hour, broadcast on CBS during the summers of 1962-1965 and 1967, was composed of one-hour specials Lucille Ball and Desi Arnaz did as a continuation of I Love Lucy repackaged with new opening credits.
 * The American version of Whose Line Is It Anyway? began its life as a 6-week-long Summer Replacement Series in 1998 before getting promoted to a full series.
 * According to The Other Wiki, Wide World of Sports "was intended to be a fill-in show for a single summer season, until the start of fall sports seasons, but became unexpectedly popular."
 * The Sonny & Cher Comedy Hour originally began as a summer replacement series for CBS in 1971 but had such high ratings that it was brought back in the fall with a permanent spot on the schedule; it lasted for three years, until Sonny and Cher's separation in 1974 torpedoed the show.

Radio

 * The Phil Silvers Show, the 1947 summer replacement for Philco Radio Time with Bing Crosby.
 * The Ray Bolger Show, the 1945 replacement for The Comedy Caravan, starring Jimmy Durante and Gary Moore.
 * Podcast Playlist, a 2015 summer replacement on CBC Radio 1 that went on to become a regular series. It plays more than just CBC podcasts - or, at least, it did before the COVID-19 pandemic made it nearly impossible to coordinate getting broadcast rights to the podcasts that they air.
 * The Frantics' first radio show, Frantic Times, began as a brief summer replacement for The Royal Canadian Air Farce but eventually graduated to its own permanent slot.
 * This Is That started as a Summer Replacement Series on CBC Radio 1 in 2010 and got a regular timeslot in 2011. The show ran until December 2018.

Web Animation

 * RWBY Chibi is this for RWBY starting in 2016.