A common misconception is that the broadcasting networks -- ABC, CBS, Fox and NBC -- own all the stations airing their programming nationwide. In reality, they only own a handful of stations.
Most local stations are owned by other companies or even private individuals. Those stations are affiliates of a network.
A network and an affiliate station have a contract for a set number of years that obligates the station to air the network's programming. For example, KSDK in St. Louis is an affiliate of NBC and airs that network's programming even though it is owned by media giant Gannett.
Usually, when an affiliate agreement expires, the network and the local station owner simply sign another one. The viewers at home aren't even aware of this process.
But in the 1990s, viewers in many U.S. cities, including some major media markets, witnessed a huge affiliation shift as Fox sought to beef up its network. In St. Louis, the ABC station KTVI became a Fox affiliate, leaving ABC searching for another station to air its programming.
KTVI was eventually bought by Fox, which made it an o&o station. That's the term used when a network owns and operates a local station.
After a few years of being a Fox o&o, the network sold KTVI to another company. That means that once again, the station is a Fox affiliate.
