Reuben C. Fine (October 11, 1914 – March 26, 1993) was an American chess player, psychologist, university professor, and author of many books on both chess and psychology. He was one of the strongest chess players in the world from the mid-1930s until his retirement from chess in 1951. He was granted the title of International Grandmaster by FIDE in 1950, when titles were introduced.

Fine's best result was his equal first place in the 1938 AVRO tournament, one of the strongest tournaments of all time. After the death of world champion Alexander Alekhine in 1946, Fine was one of six players invited to compete for the World Championship in 1948. He declined the invitation, however, and virtually retired from serious competition around that time, although he did play a few events until 1951.

Fine won five medals (four gold) in three Chess Olympiads. He won the US Open all seven times he entered (1932, 1933, 1934, 1935, 1939, 1940, 1941). He was the author of several chess books, covering endgame, opening, and middlegame.

Fine was born in the Bronx, New York City to Russian Jewish parents Jacob and Bertha (Nedner) Fine. He had a sister, Evelyn (born in 1912), and was raised by his mother alone from the age of two. An uncle taught him chess when he was eight.

Fine began chess as a young teenager at the famous Manhattan Chess Club, where he hustled for nickels, until he was asked to stop; he used the money to help feed his family. Afterwards he moved to the rival Marshall Chess Club in New York City, stomping grounds for many famous players, such as Bobby Fischer, later on. At this stage of his career, Fine played a great deal of blitz chess, and he eventually became one of the best blitz players in the world. By the early 1930s, he could nearly hold his own in blitz chess against the then world champion Alexander Alekhine, although Fine admitted that the few times he played blitz with Alekhine's predecessor José Raúl Capablanca, the latter beat him "mercilessly".

Fine's first significant master-level event was the 1930 New York Young Masters tournament, which was won by Arthur Dake. He narrowly lost a 1931 stakes match to fellow young New York master Arnold Denker.

Fine placed second at the 1931 New York State Championship with a score of 8/11, half a point behind Fred Reinfeld. Fine won the 15th Marshall Chess Club Championship of 1931 with 10½/13, half a point ahead of Reinfeld. He defeated Herman Steiner by 5½–4½ at New York 1932; this was the first of three matches between them.

At 17, Fine won his first of seven US Opens at Minneapolis 1932 with 9½/11, half a point ahead of Samuel Reshevsky; this tournament was known as the Western Open at the time. Fine played in his first top-class international tournament at Pasadena 1932, where he shared 7th–10th with 5/11; the winner was world champion Alexander Alekhine. Fine repeated as champion in the 16th Marshall Club Championship, held from October to December 1932, with 11½/13, 2½ points ahead of the runner-up.