Initially, Sigmund Freud developed a talking cure called psychoanalysis; then he wrote about his therapy and popularized psychoanalysis. After Freud, many different disciplines splintered off. Some of the more common therapies include: psychodynamic psychotherapy, transactional analysis, cognitive behavioral therapy, gestalt therapy, body psychotherapy, family systems therapy, person-centered psychotherapy, and existential therapy. Hundreds of different theories of psychotherapy are practiced (Norcross, 2005, A new therapy is born in several stages. After being trained in an existing school of psychotherapy, the therapist begins to practice. Then, after follow up training in other schools, the therapist may combine the different theories as a basis of a new practice. Then, some practitioners write about their new approach and label this approach with a new name.A pragmatic or a theoretical approach can be taken when fusing schools of psychotherapy. Pragmatic practitioners blend a few strands of theory from a few schools as well as various techniques; such practitioners are sometimes called eclectic psychotherapists and are primarily concerned with what works. Alternatively, other therapists consider themselves to be more theoretically grounded as they blend their theories; they are called integrative psychotherapists and are not only concerned with what works, but why it works (Norcross, 2005, p. 8).

For example, an eclectic therapist might experience a change in their client after administering a particular technique and be satisfied with a positive result. In contrast, an integrative therapist is curious about the "why and how" of the change as well. A theoretical emphasis is important: for example, the client may only have been trying to please the therapist and was adapting to the therapist rather than becoming more fully empowered in themselves.

The first route to integration is called common factors and "seeks to determine the core ingredients that different therapies share in common" (Norcross, 2005, p. 9). The advantage of a common factors approach is the emphasis on therapeutic actions that have been demonstrated to be effective. The disadvantage is that common factors may overlook specific techniques that have been developed within particular theories. Common factors have been described by Jerome Frank (Frank & Frank, 1991), Bruce Wampold (Wampold & Imel, 2015), and Miller, Duncan and Hubble (2005). Common factors theory asserts it is precisely the factors common to the most psychotherapies that make any psychotherapy successful.

Some psychologists have converged on the conclusion that a wide variety of different psychotherapies can be integrated via their common ability to trigger the neurobiological mechanism of memory reconsolidation in such a way as to lead to deconsolidation (Ecker, Ticic & Hulley 2012; Lane et al. 2015; Welling 2012—but for a more hesitant view of the role of memory reconsolidation in psychotherapy see the objections in some of the invited comments in: Lane et al. 2015).

The second route to integration is technical eclecticism which is designed "to improve our ability to select the best treatment for the person and the problem…guided primarily by data on what has worked best for others in the past" (Norcross, 2005, p. 8). The advantage of technical eclecticism is that it encourages the use of diverse strategies without being hindered by theoretical differences. A disadvantage is that there may not be a clear conceptual framework describing how techniques drawn from divergent theories might fit together. The most well known model of technical eclectic psychotherapy is Arnold Lazarus' (2005) multimodal therapy. Another model of technical eclecticism is Larry E. Beutler and colleagues' systematic treatment selection (Beutler, Consoli, & Lane, 2005).