The Dred Scott Decision was a landmark ruling by the United States Supreme Court in 1857 that declared African Americans, whether enslaved or free, were not American citizens and could not sue in federal court. The case originated when Dred Scott, an enslaved African American man, sued for his and his family's freedom on the basis that they had lived in free territories and states where slavery was prohibited.

However, Chief Justice Roger B. Taney and the majority of the Supreme Court ruled against Scott, stating that African Americans were not considered citizens under the U.S. Constitution, and therefore had no standing to bring a lawsuit. This decision not only denied Scott and his family their freedom, but also effectively invalidated the Missouri Compromise of 1820, which had restricted slavery in certain territories.

The Dred Scott Decision was a significant blow to the abolitionist movement and further entrenched the institution of slavery in America. It is considered one of the most infamous and controversial rulings in the history of the Supreme Court and heightened tensions between the North and South in the lead-up to the Civil War.