Bonanza is an American Western television series that ran on NBC from September 12, 1959, to January 16, 1973. Lasting 14 seasons and 431 episodes, Bonanza is NBC's longest-running Western, the second-longest-running Western series on American network television (behind CBS's Gunsmoke), and one of the longest-running, live-action American series. The show continues to air in syndication. The show is set in the 1860s and centers on the wealthy Cartwright family, who live in the vicinity of Virginia City, Nevada, bordering Lake Tahoe. The series initially starred Lorne Greene, Pernell Roberts, Dan Blocker and Michael Landon and later featured (at various times) Guy Williams, David Canary, Mitch Vogel and Tim Matheson. The show is known for presenting pressing moral dilemmas.

The title "Bonanza" is a term used by miners in regard to a large vein or deposit of silver ore, from Spanish bonanza (rich ore body) and commonly refers to the 1859 revelation of the Comstock Lode of rich silver ore mines under the town of Virginia City, not far from the fictional Ponderosa Ranch that the Cartwright family operated. The show's theme song, also titled "Bonanza", became a hit song. Only instrumental renditions, without Ray Evans's lyrics, were used during the series's long run.

In 2002, Bonanza was ranked No. 43 on TV Guide's 50 Greatest TV Shows of All Time, and in 2013 TV Guide included it in its list of The 60 Greatest Dramas of All Time. The time period for the television series is roughly between 1861 (Season 1) and 1867 (Season 13) during and shortly after the American Civil War, coinciding with the period Nevada Territory became a U.S. state.

During the summer of 1972, NBC aired reruns of episodes from the 1967–1970 period in prime time on Tuesday evening under the title Ponderosa.