Hopalong Cassidy is an American Western television series that ran from 1949 to 1952 on NBC, starring William Boyd as Hopalong Cassidy, a fictional gunslinger who had been created by writer Clarence E. Mulford. It was the first Western television series. The series began as simply broadcasts of edited versions of previous Hopalong Cassidy films, all of which had starred Boyd (66 such films had been produced between 1935 and 1948). Eventually, the series transitioned to original episodes, with a new cast of characters and actors, notably Edgar Buchanan as Hopalong's sidekick Red Connors. The show was created and produced by Boyd.

Hopalong Cassidy was a hit, especially among children, and helped lead to a wave of other Western TV series, including The Gene Autry Show and The Roy Rogers Show. It also did well in merchandising, including spawning the first TV series-themed lunchbox.