What subject did Alan Turing study at Cambridge University?

Alan Turing studied mathematics at Cambridge University. He attended King's College, Cambridge, from 1931 and completed the university's mathematics course with first-class honours in 1934.

Turing's Cambridge education gave him the foundation for work that later reshaped mathematics and computer science. His undergraduate dissertation concerned the Gaussian error function and included a proof related to the central limit theorem. He subsequently continued with Part III of the Mathematical Tripos, completing it in 1937.

A common mix-up is to answer “logic” or “computer science.” Turing made major contributions to mathematical logic and is widely regarded as a founder of theoretical computer science, but those were areas of his later research rather than the subject named in this question. Cambridge did not yet offer computer science as a modern standalone degree in Turing's student years.