Marshall Hall Jr. (17 September 1910 – 4 July 1990) was an American mathematician who made significant contributions to group theory and combinatorics.

He studied for a year at Cambridge University under a Henry Fellowship working with G. H.

[2] He returned to Yale to take his Ph.D. in 1936 under the supervision of Øystein Ore.[3][4] He worked in Naval Intelligence during World War II, including six months in 1944 at Bletchley Park, the center of British wartime code breaking.

His book Combinatorial Theory came out in a second edition in 1986, published by John Wiley & Sons.

Hall's work[6] on continued fractions showed that the Lagrange spectrum includes all numbers greater than 6.