American Slavery as It Is: Testimony of a Thousand Witnesses is a book written by the American abolitionist Theodore Dwight Weld, his wife Angelina Grimké, and her sister Sarah Grimké, which was published in 1839.

Theodore Dwight Weld was one of the architects of the American abolitionist movement during its formative years from 1830 to 1844, playing a role as writer, editor, speaker, and organizer. He is best known for his co-authorship of the authoritative compendium American Slavery as It Is: Testimony of a Thousand Witnesses, published in 1839. Harriet Beecher Stowe partly based Uncle Tom’s Cabin on Weld's text; the latter is regarded as second only to the former in its influence on the antislavery movement. Weld remained dedicated to the abolitionist movement until slavery was ended by the Thirteenth Amendment to the United States Constitution in 1865.