Frank Leslie's Illustrated Newspaper, later renamed Leslie's Weekly, was an American illustrated literary and news magazine founded in 1855 and published until 1922. It was one of several magazines started by publisher and illustrator Frank Leslie.

Throughout its existence, the weekly provided illustrations and reports—with wood engravings, lithographs and steel engravings based on sketches and photography, beginning with daguerreotypes and later with more advanced forms of photography—of wars from John Brown's raid at Harpers Ferry and the Civil War to the Spanish–American War and the First World War - and numerous other articles of topical interest.

Frank Leslie was the pen name of Henry Carter (1821–1880), the son of a well-to-do English glovemaker. Carter had taken up the art of wood engraving over his father's objection and emigrated to New York City, arriving in 1848 and immediately adopting "Frank Leslie" as his pseudonym. Unable to find a position as an illustrator with an established newspaper, he opened his own business, an engraving shop on Broadway.

One of Leslie's early clients was promoter P. T. Barnum, who commissioned Leslie to produce a posh illustrated concert program for singer Jenny Lind in 1849. Additional work was done for Barnum for another Lind tour in 1850 and 1851. When Barnum decided to launch a publication called The Illustrated News in 1853, he turned to Leslie, hiring him as chief engraver for the short-lived publication, which failed within its first year of existence.

Leslie decided to begin publishing on his own, launching two new periodicals in 1854—Frank Leslie's Ladies' Gazette of Fashion, a fashion-oriented newspaper, and Frank Leslie's Journal of Romance, an illustrated fiction magazine. Both of these publications proved to be financially lucrative, and in 1855, Leslie added a third publication, an illustrated news weekly called Frank Leslie's Illustrated Newspaper.

The first years of Frank Leslie's Illustrated Newspaper were difficult, with the nation undergoing a business crisis in 1857. The drama of the massive American Civil War in 1861, though, ensured the success of Leslie's Newspaper, as tens of thousands of readers turned to Leslie's and the upstart Harper's Weekly for their sometimes lurid illustrations of the bloody conflict. A Leslie's freelancer, James R. O'Neill, is believed to have been the only Civil War correspondent killed in action in the Civil War.

No daily newspaper in America consistently carried illustrations until the launch of The Daily Graphic in 1873, by which time Leslie's Newspaper was a massive and prosperous concern, employing more than 300 people, including 70 illustrators, as part of a publishing empire which by now spanned seven publications.

Leslie's Newspaper averaged 16 pages and was frequently accompanied by supplements or expanded into special thematic editions. Content strove to be timely, focusing on the newsworthy events of the previous week, often within days of its occurrence, a novelty for the era. Art was produced by teams, with initial sketches selected by an editor and turned over to an illustrator, who produced an outline drawing. The outline was then applied to a block consisting of multiple layers of Turkish boxwood and additional detail added by specialized artists.