The following notes were made by Professor John Eccles of five lectures (and two informal talks) given by Karl Popper dur-ing a visit to the University of Otago in May 1945. The notes were written up, cyclostyled and distributed by John Eccles, who used the results of Popper’s analysis of science in his own research, and who later shared a Nobel Prize in Physiology and Medicine. Thus, with a world-leading philosopher of science and an eventual Nobel Prize winner, we have in one set of notes an important part of the history of early high level research in New Zealand.