Sigmund Freud, the father of psychoanalysis, was a physiologist, medical doctor, psychologist and influential thinker of the early twentieth century. Working initially in close collaboration with Joseph Breuer, Freud elaborated the theory that the mind is a complex energy-system, the structural investigation of which is the proper province of psychology. He articulated and refined the concepts of the unconscious, infantile sexuality and repression, and he proposed a tripartite account of the minds structureall as part of a radically new conceptual and therapeutic frame of reference for the understanding of human psychological development and the treatment of abnormal mental conditions. Notwithstanding the multiple manifestations of psychoanalysis as it exists today, it can in almost all fundamental respects be traced directly back to Freuds original work.