The impeachment of Andrew Johnson was initiated on February 24, 1868, when the United States House of Representatives resolved to impeach Andrew Johnson, the 17th president of the United States, for "high crimes and misdemeanors", which were detailed in 11 articles of impeachment. The primary charge against Johnson was that he had violated the Tenure of Office Act, passed by Congress in March 1867 over Johnson's veto. Specifically, he had removed from office Edwin Stanton, the secretary of war whom the act was largely designed to protect. Stanton often sided with the Radical Republican faction that passed the act, and Stanton did not have a good relationship with Johnson. Johnson attempted to replace Stanton with Brevet Major General Lorenzo Thomas. Earlier, while the Congress was not in session, Johnson had suspended Stanton and appointed General Ulysses S. Grant as secretary of war ad interim.

Johnson became the first American president to be impeached on March 2–3, 1868, when the House formally adopted the articles of impeachment and forwarded them to the United States Senate for adjudication. The trial in the Senate began three days later, with Chief Justice Salmon P. Chase presiding. On May 16, the Senate did not convict Johnson on one of the articles, with the 35–19 vote in favor of conviction falling one vote short of the necessary two-thirds majority. A 10-day recess was called before attempting to convict him on additional articles. On May 26, the Senate did not convict the president on two articles, both by the same margin, after which the trial was adjourned without considering the remaining eight articles of impeachment.

The impeachment and trial of Andrew Johnson had important political implications for the balance of federal legislative-executive power. It maintained the principle that Congress should not remove the president from office simply because its members disagreed with him over policy, style, and administration of the office. It also resulted in diminished presidential influence on public policy and overall governing power, fostering a system of governance which future-President Woodrow Wilson referred to in the 1880s as "Congressional Government".