Library SARC Research Paper
On Computable Numbers, with an Application to the Entscheidungsproblem
Turing's 1936 paper defining the Turing machine and the limits of mechanical computation.

Turing’s 1936 paper defining the Turing machine and proving the undecidability of the Entscheidungsproblem — the decision problem posed by David Hilbert and Wilhelm Ackermann in 1928 — founding theoretical computer science.