Psychoanalysis is a form of psychotherapy based largely on Sigmund Freud's work with psychodynamics. The main goal of therapist in psychoanalysis is to help the patient come to terms with issues locked in the sub-conscious mind.  Practitioners of psychoanalytic psychology believe that mental and behavioral disorders are due to repressed unconscious thoughts usually linked to key events during development.
The origins of the idea stems from Freud's work in the 1880s and his attempts to treat individuals diagnosed with neurotic or hysterical disorders. He came to believe that these disorders emerged because the patients were repressing taboo sexual thoughts and desires.
Psychoanalysis is not simply a recasting of Freud's ideas. Many other practitioners developed the concept beyond just repressed sexuality. Carl Jung believed there was a range of traumatic events that could lead to repression and advocated for concepts like archetypes and synchronicity. Jung was also a proponent of dream interpretation as a mechanism for understanding the patients unconscious. He also believed in a collective unconscious that dreams could tap into.
Modern day practitioners of psychoanalysis are predominantly clinically based. However, it is nowhere near as popular as it was in it prime during the mid 20th century. Some researchers in psychology are also interested in ideas of psychoanalysis. One psychoanalytic concept that has been supported by experimental evidence is the idea of psychological defensive mechanisms. However, much of psychoanalysis has not stood up to empirical investigation. Repressed sexuality, dream interpretation, a collective unconscious and many other ideas that are the back bone of psychoanalysis have all been falsified in controlled experiments.
Psychoanalysis has also been labeled as unscientific because it lacks the ability to be falsified. Karl Popper is probably one of the most significant critics in this fashion.
While empirical investigation has mostly been negative for psychoanalysis, certain elements of psychoanalytic theory have been very important to development of modern psychology. These include the realization that the mind has elements not under direct conscious control that can affect actions and behavior, and that human mental development occurs in stages.
- "The basic premise of psychoanalysis is that most psychological symptoms are the result of our unconsciously avoiding many of the unpleasant truths about ourselves. Through a detailed “psycho” analysis (i.e., analysis of our thought process and mental images) we come to learn just how we manage to deceive ourselves. The idea behind this treatment philosophy is that persons who have come to understand their own deceptions can then manage to avoid being controlled by them." Guide to Psychology