One of the most influential thinkers of the 20th century, Sir Karl Popper here examines the problems connected with human freedom, creativity, rationality and the relationship between human beings and their actions. In this illuminating series of papers, Popper suggests a theory of mind-body interaction that relates to evolutionary emergence, human language and what he calls "the three worlds." Rene; Descartes first posited the existence of two worlds--the world of physical bodies and the world of mental states. Popper argues for the existence of "world 3" which comprises the products of our human minds. He examines the interaction between mental states--hopes, needs, plans, ideologies or hypotheses--and the physical states of our brain. Popper forcefully argues against the materialism forwarded by many philosophers which denies the existence of mental states. Instead, he demonstrates that the problem of the interaction between mental and physical states remains unresolved. Knowledge and the Body-Mind Problem is based on Popper's never-before published lectures at Emory University in 1969. Popper has extensively revised the lectures but has retained their accessible format. He has also incorporated some of the discussions which followed the lectures, providing an engaging exchange between the philosopher and his audience.