Godel's Incompleteness Theorems

In 1931 Austrian logician, mathematician and philosopher Kurt Gödel published while in Vienna Über formal unentscheidbare Sätze der "Principia Mathematica" und verwandter Systeme (called in English "On Formally Undecidable Propositions of 'Principia Mathematica' and Related Systems"). That article dated November 17, 1930, which first appeared in the 1931 volume of Monatshefte für Mathematik, contained Godel's first and second incompleteness theorems. 

van Heijenoort, ed. From Frege to Gödel: A Source Book on Mathematical Logic 1879–1931 (1967) 592-617.