Abstract Sigmund Freud is one of the most important thinkers of the twentieth century because his ideas have been used in the culture today. It is unlikely that a person has never heard of or used a Freudian idea such as a Freudian slip or dream analysis. This paper focuses on Freud's revolutionary theory of psychoanalysis, its origins, and its impact on psychology today. The principles of this theory are fully explained. Sigmund Freud and Psychoanalysis Sigmund Freud was born in Freiberg, Moravia on May 6, 1856 or March 6, 1856. ...