The collection spans the whole of Popper's career. It includes drafts of his published works; drafts of substantial unpublished works, including six book-length manuscripts; and transcripts of his lectures at the London School of Economics. The voluminous correspondence with Albert Einstein, Niels Bohr and Werner Heisenberg among hundreds of others is of particular importance. Also ofinterest is the documentation of debates between Popper and Erwin Schrd̲inger especially on Ludwig Boltzmann's concept of the "arrow of time," and correspondence relating to Popper's evaluations of the position of Albert Einstein, B. Podolsky and N. Rosen regarding the philosophical implications of quantum physics for determinism and indeterminism in the natural world.