The book that the reader has in hand addresses the metaphysical problem of the mind-body relationship. The aim is to present the various theories of mind that have emerged throughout the history of philosophy. It reaffirms here the theory of the "Three Worlds Thesis" of K. Popper's "Three Worlds Thesis", with emphasis on World 3, as one of the most ingenious explanations of the problem. At the same time, the insufficiency of monisms and dualisms in trying to answer the problem is pointed out. Of course, this problem has undergone several changes in its approach, as research on the human brain has advanced considerably since the "decade of the brain" (1990). Therefore, together with the problem of the philosophy of science, it is one of the greatest problems in the history of contemporary philosophy, requiring further study.