Two Years Before the Mast is a memoir by the American author Richard Henry Dana Jr., published in 1840, having been written after a two-year sea voyage from Boston to California on a merchant ship starting in 1834. A film adaptation under the same name was released in 1946.

The term "before the mast" refers to the quarters of the common sailors, in the forecastle, in the front of the ship. His writing evidences his later sympathy with the lower classes. He later became a prominent anti-slavery activist and helped found the Free Soil Party.

In the book, which takes place between 1834 and 1836, Dana gives a vivid account of "the life of a common sailor at sea as it really is". He sails from Boston to South America and around Cape Horn to California. Dana's ship was on a voyage to trade goods from the United States for the Mexican colonial Californian California missions' and ranchos' cow hides. They traded at the ports in San Diego Bay, San Pedro Bay, Santa Barbara Channel, Monterey Bay, and San Francisco Bay.

Richard Henry Dana Jr. (1815-1882) was an American lawyer and politician from Massachusetts, a descendant of an eminent colonial family, who gained renown as the author of the American classic, the memoir Two Years Before the Mast. Both as a writer and as a lawyer, he was a champion of the downtrodden, from seamen to fugitive slaves and freedmen.