http://www.law.cornell.edu/background/impeach/impeach.htm<snip>
The Impeachment Process in a Nutshell
The House Judiciary Committee deliberates over whether to initiate an impeachment inquiry.
The Judiciary Committee adopts a resolution seeking authority from the entire House of Representatives to conduct an inquiry. Before voting, the House debates and considers the resolution. Approval requires a majority vote.
The Judiciary Committee conducts an impeachment inquiry, possibly through public hearings. At the conclusion of the inquiry, articles of impeachment are prepared. They must be approved by a majority of the Committee.
The House of Representatives considers and debates the articles of impeachment. A majority vote of the entire House is required to pass each article. Once an article is approved, the President is, technically speaking, "impeached" -- that is subject to trial in the Senate.
The Senate holds trial on the articles of impeachment approved by the House. The Senate sits as a jury while the Chief Justice of the Supreme Court presides over the trial.
At the conclusion of the trial, the Senate votes on whether to remove the President from office. A two-thirds vote by the Members present in the Senate is required for removal.
If the President is removed, the Vice-President assumes the Presidency under the chain of succession established by Amendment XXV.