John Spencer Letts (born 1934) is a United States federal judge.
Born in St. Louis, Missouri, Letts received a B.A. from Yale University in 1956 and an LL.B. from Harvard Law School in 1960. He was a Reserve Captain in the United States Army from 1956 to 1965. He was in private practice in Houston, Texas from 1960 to 1966. He was a vice president and general counsel of Teledyne in Los Angeles, California from 1966 to 1973, and was in private practice in Los Angeles from 1973 to 1975 before returning to his previous positions with Teledyne from 1975 to 1978. He returned to private practice in Los Angeles from 1978 to 1985.
on November 7, 1985, Letts was nominated by President Ronald Reagan to a new seat on the United States District Court for the Central District of California created by 98 Stat. 333. He was confirmed by the United States Senate on December 16, 1985, and received his commission on December 17, 1985. He assumed senior status on December 19, 2000.