This collection of essays on the work of Sir Karl Popper is based on the Royal Institute of Philosophy’s annual lecture series given in London from October 1994 to March 1995. Popper himself died in August 1994, shortly before the start of the lectures. His death was the cause of sadness to all of those involved in the series. Some, indeed, had been close friends of Popper over many years, and others colleagues and acquaintances, some close, some more distant. Even those unacquainted with Popper personally spoke in their lectures of the profound intellectual stimulation they had received from the study of his works.