Article One of the United States Constitution
The Constitution does not specify how impeachment proceedings are to be initiated. Until the early 20th century, a House member could rise and propose an impeachment, which would then be assigned to a committee for investigation. Presently, it is the House Judiciary Committee that initiates the process. It does this only after investigating the allegations, prepares recommendations for the whole House's consideration. If the House votes to adopt an impeachment resolution, the Chairman of the Judiciary Committee recommends a slate of "managers," whom the House subsequently approves by resolution.  These Representatives then become the prosecution team in the impeachment trial in the Senate (see Section 3, Clause 6 below).