"O Captain! My Captain!" is an extended metaphor poem written by Walt Whitman in 1865 about the death of U.S. president Abraham Lincoln. Well received upon publication, the poem was Whitman's first to be anthologized and the most popular during his lifetime. Together with "When Lilacs Last in the Dooryard Bloom'd", "Hush'd Be the Camps To-day", and "This Dust was Once the Man", it is one of four poems written by Whitman about the death of Lincoln.

During the American Civil War, Whitman moved to Washington, D.C., where he worked for the government and volunteered at hospitals. Although he never met Lincoln, Whitman felt a connection to him and was greatly moved by Lincoln's assassination. "My Captain" was first published in The Saturday Press on November 4, 1865, and appeared in Sequel to Drum-Taps later that year. He later included it in the collection Leaves of Grass and recited the poem at several lectures on Lincoln's death.

Stylistically, the poem is uncharacteristic of Whitman's poetry because of its rhyming, song-like flow, and simple "ship of state" metaphor. These elements likely contributed to the poem's initial positive reception and popularity, with many celebrating it as one of the greatest American works of poetry. Critical opinion has shifted since the mid-20th century, with some scholars deriding it as conventional and unoriginal. The poem has made several appearances in popular culture; as it never mentions Lincoln, it has been invoked upon the death of several other heads of state. It is famously featured in Dead Poets Society (1989) and is frequently associated with the star of that film, Robin Williams.