The development of quantum mechanics in the years 1900-1927 was one of the greatest conceptual transformations in the history of modern science. In this course, we still study this development, from Max Planck's first papers on black body radiation to the debates between Albert Einstein and Niels Bohr at the 1927 Solvay conference. The course will take a holistic view of this development, covering experimental breakthroughs, the development of mathematical formalism and physical concepts, as well as the broader philosophical and historical context of early 20th century Europe. Students will acquire an understanding of a scientific revolution that goes beyond well-worn stories of sudden heroic epiphanies.