Expulsion is the most serious form of disciplinary action that can be taken against a Member of Congress. Article I, Section 5 of the United States Constitution provides that "Each House [of Congress] may determine the Rules of its proceedings, punish its members for disorderly behavior, and, with the concurrence of two-thirds, expel a member." The processes for expulsion differ somewhat between the House of Representatives and the Senate. 
Censure, a less severe form of disciplinary action, is an official sanction of a member. It does not remove a member from office.
Presently, the disciplinary process begins when a resolution to expel or censure a Member is referred to the appropriate committee. In the House, this is the Committee on Standards of Official Conduct (House Ethics Committee); in the Senate, this is the Select Committee on Ethics (Senate Ethics Committee).
The committee may then ask other Representatives or Senators to come forward with complaints about the Member under consideration or may initiate an investigation into the Member's actions. Sometimes Members may refer a resolution calling for an investigation into a particular Member or matter that may lead to the recommendation of expulsion or censure.
Rule XI (Procedures of committees and unfinished business) of the Rules of the House of Representatives states that the Committee on Standards of Official Conduct can investigate allegations that a Member violated "any law, rule, regulation, or other standard of conduct applicable to the conduct of such Member ... in the performance of his duties or the discharge of his responsibilities". The Senate Select Committee on Ethics has the same jurisdiction. The committee may then report back to their whole chamber as to its findings and recommendations for further actions.
When an investigation is launched by either committee, an investigatory subcommittee will be formed. Once the investigatory subcommittee has collected evidence, talked to witnesses, and held an adjudicatory hearing, it will vote on whether the Member is found to have committed the specific actions and then will vote on recommendations. If expulsion is the recommendation then the subcommittee's report will be referred to the full House of Representatives or Senate where Members may vote to accept, reject, or alter the report's recommendation. Voting to expel requires the concurrence of two-thirds of the members. This is set out in Article 1, Section 5, Clause 2 of the United States Constitution
In the entire history of the United States Congress, 20 Members have been expelled: 15 from the Senate and 5 from the House of Representatives (of those, one member's expulsion, William K. Sebastian of Arkansas, was posthumously reversed). Censure has been a much more common form of disciplinary action in Congress over the years, as it requires a much lower threshold of votes to impose.
The great majority of those expelled — 17 members — were removed from office for their support of the Confederacy in the immediate aftermath of secession. 
- In 1861, after the Civil War had broken out, eleven Senators (including former Vice President and Kentucky Senator John C. Breckinridge) and three Representatives were expelled for supporting the Confederacy.
- In 1862, three more Representatives were expelled for supporting the Confederate States: John Bullock Clark and John William Reid of Missouri, and Henry Cornelius Burnett of Kentucky.
There have only been three other expulsions:
- In 1797, Senator William Blount of Tennessee was expelled for treason, with charges centering on a plan to incite the Creek and Cherokee to aid the British in conquering the Spanish territory of West Florida. Blount remains the only Senator to be expelled for a reason other than supporting the Confederacy.
- In 1980 Representative Michael Myers of Pennsylvania was expelled for bribes in connection with the Abscam scandal.
- In 2002, Representative Jim Traficant of Ohio was expelled after he was convicted on numerous counts of bribery, racketeering, and tax evasion.
There have been numerous other attempts to expel members of Congress. In many of those instances members under serious threat of expulsion resigned, including:
- 1862: Senator James F. Simmons, Republican of Rhode Island. On July 14, 1862, the Judiciary Committee reported that the charges of corruption against Simmons were "essentially correct"; The Senate adjourned three days later, and Simmons resigned on August 15 before the Senate could take action.
- 1906: Senator Joseph R. Burton, Republican of Kansas. Resigned after the Supreme Court upheld his conviction on charges of receiving compensation for intervening with a federal agency.
- 1922: Senator Truman H. Newberry, Republican of Michigan. On March 20, 1920, Newberry was convicted on charges of violating campaign finance laws by spending $3,750 to secure his Senate election. The Supreme Court overturned this decision on May 2, 1921 on the grounds that the Senate exceeded its powers in attempting to regulate primary elections. On January 12, 1922, the Senate voted 46-41 that Newberry was duly elected in 1918. However, after certain members resumed their efforts to unseat him, Newberry resigned on November 18, 1922, two days before the start of the third session of the 67th Congress.
- 1981: Representative Raymond F. Lederer, Democrat of Pennsylvania, was the only member of the ABSCAM scandal to win re-election. However he resigned due to "personal legal problems" a week after the House Ethics Committee recommended his expulsion for accepting a $50,000 bribe. 
- 1982: Senator Harrison A. Williams, Democrat of New Jersey, resigned after the Committee on Ethics recommended his expulsion due to his "ethically repugnant" actions in the Abscam scandal.
- 1995: Senator Bob Packwood, Republican of Oregon, resigned after the Committee of Ethics recommended his expulsion due to his gross sexual misconduct and his attempts to enrich himself through his official position.
- 2006: Representative Bob Ney, Republican of Ohio, resigned after being convicted in connection with the Jack Abramoff scandals.
There were other instances in which investigations were brought, but the defendants were exonerated, expulsion was rejected, insufficient evidence was found. or the member's term expired:
- 1808: Senator John Smith, Democratic-Republican of Ohio, was implicated in the Aaron Burr-led conspiracy to invade Mexico and create a new country in the west. Senator John Quincy Adams of Massachusetts led the attempt to expel Smith from the Senate while Francis Scott Key defended Smith before the Senate. Expulsion failed 19 to 10, less than the two-thirds majority needed. At request of the Ohio Legislature, Smith resigned two weeks after the vote.
- 1856: Congressman Preston Brooks, Democrat of South Carolina, beat Senator Charles Sumner with a cane. For this incident, he avoided expulsion but resigned; he was then re-elected by the people of South Carolina, who considered him a hero.
- 1862: The expulsion of Senator Lazarus W. Powell, Democrat of Kentucky, was sought for support for Confederate rebellion. Unlike the three Senators expelled for that reason the same year and the eleven Senators the previous year, Powell was not expelled.
- 1873: Senator James W. Patterson, Republican of New Hampshire, was accused of corruption, and a Senate select committee recommended expulsion on February 27. On March 1, a Republican caucus decided that there was insufficient time remaining in the session to deliberate the matter. Patterson's term expired March 3, and no further action was taken.
- 1893: Senator William N. Roach, Democrat of North Dakota, was accused of embezzlement that had allegedly occurred 13 years earlier. After extensive deliberation, the Senate took no action, assuming that it lacked jurisdiction over members' behavior before their election to the Senate.
- 1905: Senator John H. Mitchell, Republican of Oregon, was indicted on corruption charges on January 1, 1905, and was convicted on July 5 of that year, during a Senate recess. He died on December 8, while his case was still on appeal and before the Senate, which had convened on December 4, could take any action against him.
- 1907: Senator Reed Smoot, Republican of Utah, a leader in the LDS Church, was the subject of a two-year investigation by the Committee on Privileges and Elections, which found that Smoot was not due his seat in the Senate because he was "a leader in a religion that advocated polygamy and a union of church and state, contrary to the U.S. Constitution."  Smoot's expulsion failed by a vote of 27-43 after the Senate decided that he fit the constitutional requirements to be a Senator.
- 1919: Senator Robert M. La Follette, Sr., Republican of Wisconsin, was accused of disloyalty after a 1917 speech he gave in opposition to U.S. entry into World War I. The Committee on Privileges and Elections recommended that La Follette not be expelled and the Senate concurred in a 50-21 vote.
- 1924: Senator Burton K. Wheeler, Democrat of Montana, was indicted for conflict of interest, specifically acting as a lawyer, while a senator, in cases in which the U.S. was a party. A Senate committee, however, found that his dealings related to litigation before state courts and that he received no compensation for any service before federal departments. The Senate exonerated him by a vote of 56-5. 
- 1934: The Committee on Privileges and Elections, jointly considering the case of Senators John H. Overton, Democrat, and Huey P. Long, Democrat, both of Louisiana, determined that the evidence to support charges of election fraud were insufficient to warrant further consideration.
- Impeachment in the United States
- List of United States senators expelled or censured
- List of United States Representatives expelled, censured, or reprimanded
- Resignation from the United States Senate (lists several senators who resigned under an ethical cloud)
- Resignation from the United States House of Representatives
- List of federal political scandals in the United States
- Brown, Cynthia; Garvey, Todd (January 11, 2018). Expulsion of Members of Congress: Legal Authority and Historical Practice (PDF). Washington, DC: Congressional Research Service. Retrieved 27 January 2018.
- Good, Chris (December 3, 2010). "Five Ways to Get Kicked Out of Congress". The Atlantic. Retrieved July 10, 2018.
- "Exit Mr. Lederer". The New York Times. May 3, 1981.
- "4 Briefing on Expulsion and Censure". U.S. Senate. 30 May 2014. Retrieved 28 September 2014.
- "Burton Wheeler, former Senator for Montana - GovTrack.us". GovTrack.us. Retrieved 2018-07-10.
- Maskell, Jack. "Expulsion, Censure, Reprimand, and Fine: Legislative Discipline in the House of Representatives", Congressional Research Service, April 16, 2002.
- Maskell, Jack. "Recall of Legislators and the Removal of Members of Congress from Office", Congressional Research Service, March 20, 2003.
- "Senate History on Expulsion and Censure."
- Sorokin, Ellen. "In Congress' 213-year history, expulsion 'exceedingly rare'", The Washington Times, July 25, 2002.