The United States Open Championship, commonly known as the U.S. Open, is the annual open golf tournament of the United States. It is the second of the four major championships in golf and is on the official schedule of both the PGA Tour and the European Tour. It is staged by the United States Golf Association in mid-June, scheduled such that the final round is always played on the third Sunday, which is Father's Day. From 2008, it will also be an official money event on the Asian Tour, with 50% of Asian Tour members' earnings counting towards the Order of Merit.

The U.S. Open is staged at a variety of courses, set up in such a way that scoring is very difficult with a premium placed on accurate driving. U. S. Open play is characterized by tight scoring at or around par by the leaders, with the winner emerging at just under par. A U.S. Open course is seldom beaten severely, and there have been many over-par wins. Normally, an Open course is longer than normal and will have a high cut of rough, hilly greens , and pinched fairways. Some courses that are attempting to get into the rotation for the U.S. Open will normally be rebuilt to have these features. Rees Jones is the most notable of the "Open Doctors" who take on these projects.

The U.S. Open is open to any professional, or to any amateur with an up-to-date USGA Handicap Index not exceeding 1.4. Players may obtain a place by being fully exempt or by competing successfully in qualifying. The field is 156 players.