In 1936 Saul Rosenzweig (19072004) published a scientific paper concluding that psychotherapies of different theoretical and practical orientations all produce equivalent effectiveness-a conclusion that remains unchanged today despite 75 years of empirical research seeking to find differential effectiveness for different forms of psychotherapy treatment. What is less well know, however, is that despite equivalent effectiveness of therapy brand names, there is considerable variation in effectiveness between individual therapists. It is therefore fitting that this book begins with a message from Rosenzweig, which sets the scene for a very different volume from the first edition. The first edition (1999), edited by Hubble, Duncan and Miller, quickly became a classic text in the field because it took Rosenzweig's conclusion, and then turned it into a set of principles to help therapists become more effective. The idea at the time was that therapists should capitalise on four common factors: (1) mobilise the client's life circumstances and environment; (2) enhance the therapy relationship; (3) create an atmosphere of hope and expectation of change; and (4) use therapy techniques in the service of helping the client to make their own changes. These principles were patched together based on past research to create an argument for change.