Even though Nixon wasn't impeached, the events surrounding the investigation had a significant impact on the U.S. government. For instance, the Saturday Night Massacre resulted in the passage of the Ethics in Government Act of 1978, portions of which are still in effect today.
Richard Nixon was not actually impeached but he often comes up in discussions about impeachment. The House of Representatives initiated impeachment proceedings against Nixon and adopted three articles of impeachment on July 30, 1974. Nixon resigned on August 9, 1974, before the charges could be read to the House and voted on.
The resources below are about the events leading up to the House initiating proceedings.