The Lincoln–Douglas debates were a series of seven debates between Abraham Lincoln, the Republican Party candidate for the United States Senate from Illinois, and incumbent Senator Stephen Douglas, the Democratic Party candidate. The debates focused on slavery, specifically whether it would be allowed in the new states to be formed from the territory acquired through the Louisiana Purchase and the Mexican Cession. Douglas, as the Democratic candidate, held that the decision should be made by the residents of the new states themselves rather than by the federal government (popular sovereignty). Lincoln argued against the expansion of slavery, yet stressed that he was not advocating its abolition where it already existed.

Douglas was re-elected by the Illinois General Assembly, 54–46. But the publicity made Lincoln a national figure and laid the groundwork for his 1860 presidential campaign. As part of that endeavor, Lincoln edited the texts of all the debates and had them published in a book. It sold well and helped him receive the Republican Party's nomination for president at the 1860 Republican National Convention in Chicago.