The concept of dissociation has been reviewed and redefined. It was also compared with other mental mechanisms. In the past, the process of dissociation and the content of the dissociation have often been lumped together although they are separate frames of reference. Moreover, very different psychic elements may be dissociated including memories, affects, and psychic structure. Dissociation is an important mental mechanism that plays a very significant role in people's adaptational efforts. In addition, dissociation is the underlying mechanism in a number of defense mechanisms. Repression, intellectualization, splitting, and other defense mechanisms rely upon dissociation to accomplish their specific tasks. Dissociation is thus believed to be the underlying and basic mechanism of many aspects of mental functioning.