In the United States, Federal Communications Commission (FCC) regulations limit the number of network-owned stations as a percentage of total national market reach. As such, networks tend to have O&Os only in the largest media markets (such as New York City and Los Angeles), and rely on affiliates to carry their programming in other markets. However, even the largest markets may have network affiliates in lieu of O&Os. For instance, Tribune Broadcasting's WPIX serves as the New York City affiliate of The CW, which does not have an O&O in that market. On the other hand, several other television stations in the same market – WABC-TV (ABC), WCBS-TV (CBS), WNBC (NBC), WNJU (Telemundo), WNYW (Fox), WWOR-TV (MyNetworkTV), WPXN-TV (Ion Television), WXTV-DT (Univision) and WFUT-DT (UniMás) – are O&Os.
In 2009, after many years of decline, the era of secondary affiliations to multiple major networks (once common in communities where fewer stations existed than networks seeking carriage) finally came to an end at the smallest-market U.S. station, KXGN-TV in Glendive, Montana (which was affiliated with both CBS and NBC). The digital conversion allowed KXGN to carry CBS and NBC programming side-by-side on separate subchannels, essentially becoming a primary affiliate of both networks.
Affiliate marketing is commonly confused with referral marketing, as both forms of marketing use third parties to drive sales to the retailer. The two forms of marketing are differentiated, however, in how they drive sales, where affiliate marketing relies purely on financial motivations, while referral marketing relies more on trust and personal relationships.