Hilbert gave a two-semester course on the “Foundations of Physics” in the summer semester 1916 and the following winter semester 1916/17. In this Chapter we present the Ausarbeitungen of this two-part course. While Hilbert was preparing his “First Communication” on the “Foundations of Physics” for publication (Hilbert 1915, this Volume pp. 28–46), classes had resumed in Göttingen for the winter term of 1915/16. But Hilbert did not lecture on relativity during this semester. Instead, he lectured on differential equations (Hilbert 1915). Thus, in contrast to his lectures and publications on radiation theory and his second note, the publication of his first note is not an example of Hilbert’s teaching on a topic prior to or simultaneous with his current research concerns. But in the following summer term of 1916, Hilbert started to lecture on relativity theory. The lecture was announced as “Einleitung in die Prinzipien der Physik” and took place on Thursdays, 9–11 a.m. As is clear from the handwritten equations, Hilbert’s summer lectures were worked out by the Swiss mathematician and physicist Richard Bär, who had come to work as Hilbert’s assistant some time around Easter 1916.