Impeachment (Fr. empechement, hindrance, obstruction), the accusation and prosecution, in a legislative body, of a person for.treason or other high crimes. By the law of England, any member of the house of commons may impeach any other member of the house, or any lord of parliament, or indeed any other officer of the realm. Upon such impeachment being made, the house of commons, if they see lit, exhibit articles of impeachment before the house of lords, and appoint managers to sustain the charge and conduct the trial; and upon the trial, the same rules of evidence, in general, are in force as in trials in the ordinary courts of justice. This is a very solemn procedure, it being a prosecution before the supreme court of criminal jurisdiction for the whole realm, by the grand inquest thereof. It has been most frequently used against the king's ministers; and in order to take the trial from the power of the king, it is provided by law that the impeachment is not abated either by the prorogation or dissolution of parliament.

The latest and best known cases are those of Warren Hastings (1788) and of Lord Melville (1806). In the United States, impeachment is a written charge and accusation by the house of representatives of the United States, made to the senate of the United States, against an officer thereof; or, in a state, it is such an accusation of an officer, by the representatives of the state, before the senate. The proceedings, rules, and practice in cases of impeachment in this country are borrowed from the common law of England, excepting so far as they are affected by the constitution or statutes of the United States, or of the several states. The constitution of the United States declares (art. i., sec. 2) that the house of representatives shall have the sole power of impeachment, and (art. i., sec. 3) that the senate shall have the sole power to try all impeachments. By art. ii., sec. 4, the persons made liable to impeachment are the president, the vice president, and all civil officers of the United States. The offences for which a person may be impeached are (art. ii., sec. 4) "treason, bribery, and other high crimes and misdemeanors." The constitution defines treason, but what acts are impeachable offences under the other words employed must be determined by the judgment of the two houses.

They would probably be guided, but not governed, by the rules of the common law and the practice of parliament. - The method of procedure is substantially as follows: A resolution is offered by some member of the house, charging the party to be impeached with his supposed offence, and either demanding at once his impeachment, or, what is more common, providing for a committee of inquiry. If the resolution is passed, and if a committee of inquiry reports in favor of an impeachment, and their report is adopted, a committee (the same or another) is instructed to impeach the accused before the senate, and demand that that body make due provision for the trial, and inform the senate that articles of impeachment will be prepared by the house and exhibited before the senate. The same or another committee is intrusted to prepare articles of impeachment, which, being approved by the house, are transmitted to the senate by a committee appointed to conduct the trial on the part of the house, who are usually styled the managers of the impeachment.

Due process summoning the accused then issues from the senate, and is served by its sergeant-at-arms; and on the day therein appointed, the senate resolves itself into a court of impeachment, all the senators being sworn to do justice according to the constitution and the laws. The person thus impeached is then called upon to appear and answer. If he makes default, the senate proceeds ex parte. If he appears and denies the charges, and puts himself on trial (and he may appear by attorney), an issue is formed, and a time is appointed for the trial, which thereafter proceeds according to law and usage, and much in the same way as in common judicial trials. If any questions arise among the senators, who now act as judges, they are considered with closed doors, and are decided by yeas and nays, and only the decision is made public. Art. i., sec. 2, of the constitution of the United States, provides that no person shall be convicted without the concurrence of two thirds of the members. The most noted cases of impeachment in the United States are those of Judge Samuel Chase, of the federal supreme court (1804), and President Andrew Johnson (1868).