U.S. Open Chess Championship

The U.S. Open Championship is an open national chess championship that has been held in the United States annually since 1900.

Through 1938, the tournaments were organized by the Western Chess Association and its successor, the American Chess Federation (1934–1938). The United States Chess Federation (USCF) has run the tournament since 1939.

In the early years of the tournament, the number of entrants was small, and play was conducted as round robins with preliminaries, Championship Finals, and Consolation Finals.

It remained a round robin through a semi-invitational phase, but gradually introduced preliminary and final sections to accommodate more players.

An important innovation came in 1946, as the Swiss System was used for the first time to determine placement from the preliminary to the various final sections.

Starting in 1947, there have not been preliminary rounds; the U.S. Open has been held as a single section paired by the Swiss system. For many years, the tournament had 12 or 13 rounds and lasted two weeks. After experimentation with various less-demanding formats, in recent years it has usually been 9 rounds; the 2015 tournament was 9 rounds in 9 days.

Tournament participation grew through the 1950s and 1960s. Milwaukee 1953 had 181 entrants, setting a new record for the tournament. Cleveland 1957 had 184 players, and San Francisco 1961 set another attendance record with 198 players. The 1963 Open at Chicago had 266 entries, making it the largest chess tournament held in the United States to that time. The tourney was slightly smaller at Boston in 1964, with a field of 229.

The 1983 Open at Pasadena was the largest ever, at 836 official entries; it also featured the participation of Viktor Korchnoi, who had played in the last two World Championship matches.

In the 2000s, the fields were over 400 to 500 entries. The tournament began in some editions to decline both in attendance and importance, and often many winners are involved in a tie for first, especially since the mid 1990s.

The cash prizes awarded were large for their time and added to the tournament's popularity. In 1962, the entry fee was $20, with a first prize of $1000, second prize $500, third $300, fourth $200, fifth $100, sixth through tenth $50 and eleventh through fifteenth $25. The Women's Open Champion won $200, and the Women's runner-up $100. Additional cash prizes were awarded to the top women, the top junior, and for the best scores in the Expert, A, B, and C classes. The 2016 guaranteed prize fund was $40,000, with $8000 for first place.

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