The first document that provides insight into Hilbert’s concern with Einstein’s general theory of relativity and with a unified field theory of the foundations of physics is perhaps also his best known. It is his “First Communication” on the “Foundations of Physics” (Hilbert 1915). This note was submitted to the Göttingen Academy of Science for publication in its Proceedings on 20 November 1915. It was followed by a “Second Communication” that was submitted to the Academy a year later on 23 December 1916 (Hilbert 1917). In 1924, Hilbert combined both papers into a single article and made some revisions before it was reprinted in the Mathematische Annalen (Hilbert 1924). Today, Hilbert’s work in general relativity and unified field theory is known primarily through this 1924 paper, which was reprinted again with a few, but very minor changes, in the third volume of his Gesammelte Abhandlungen (Hilbert 1935, pp. 258–289).