Albert Schweitzer said 'All the problems of religion ultimately go back to the one - the experience I have of God within myself differs from knowledge concerning Him which I derive from the world ... In the world He is impersonal force; within me, He reveals Himself as Personality'. In his earlier books, Dr Crookall dealt with the most important of psychical experiences, namely, out-of-the-body experiences, popularly called astral projections. These are, he says, natural and normal to mankind. This work is concerned with cosmic and mystical experiences, the 'highest' and most significant of which we are capable. These are also natural and normal to mankind. In the First Part, a large number of experiences of at-one-ment are assembled and classified, preparatory to a consideration of their incidence and nature. Some people have at-one with inanimate objects, others with animate objects (nature), still others with people, and many with God. These various groups are shown to overlap - there is, says Crookall, a complete and unbroken spectrum beginning with minerals and ending with God. It is clear that at-one-ment with God is not, as some writers have supposed, essentially distinct from at-one-ment with nature. On the basis of this, the author agrees with Dr Raynor Johnson and the Revd Sidney Spencer: the latter concluded 'Cosmic consciousness is the natural complement of the experience of union with God'. The Second Part of the book deals with descriptions of at-one-ment that have hitherto been entirely neglected by writers on this important subject, namely, those of 'communicators', the supposed dead. Some supposed dead 'communicators' are shown to describe at-one-ment with inanimate objects, others with nature, with people, and still others with God. Again, these groups overlap to form an unbroken spectrum of experience, as in the experiences of the living - a strong suggestion of surviving souls. In point of fact, Crookall notes that mystical experiences seem to be more frequent among the dead than the living! This, of course, might have been expected. Human mystical experiences are here considered, for the first time, in relation to the correlation suggested in the author's first book.