Abstract Theory and research on emotion in both psychology and psychotherapy are reviewed to demonstrate the importance of emotion in human functioning and psychotherapeutic change. A proposal is made for the importance of integrating empirically supported emotion-focused change processes into psychotherapeutic work. Five principles of change in the emotion domain-emotion awareness; expression; regulation; reflection on emotion; and the more novel principle of emotion transformation, by which emotion is changed by emotion-are offered as processes of change that are rapidly gathering empirical support. The result of emotion coming of age will be the expansion of theories of dysfunction and of treatment to include emotion-focused coping and emotional processes of change. Keywords: emotion, emotion-focused therapy, awareness, regulation transformation This article reviews both the evolving understanding of the role of emotion in human functioning and the evidence for the important role of emotion in psychotherapy, and a set of empirically grounded principles of emotional change is proposed. Given that emotion now is seen as information, as signalling the significance of the situation to a person's well being, and given that affect regulation is seen as a key human motivation, it has become clear that emotion needs to be focused on, accepted and worked with directly in therapy to promote emotional change. (Foa, Riggs, Massie, & Yarczower, 1995; Fosha, 2000; Greenberg, 2002; Goldman, Greenberg, & Angus, in press; Linehan et al., 2002; Samoilov & Goldfried, 2000). The idea that accessing and exploring painful emotions, within the context of a secure therapeutic relationship, leads to therapeutic change has been widely held by several schools of psychotherapy (Bowlby, 1980; Kohut, 1977; Rogers, 1951; Peris, 1969) but has been difficult to prove. However over the past decade, newer therapeutic approaches that treat affect as a primary target of intervention, within the context of an empathie relationship, have been developed, tested, and shown to be effective in the treatment of affective disorders, personality disorders, and trauma (Goldman et al., in press; Svartberg, Stiles, & Seltzer, 2004). Emotions as an Adaptive Resource Until recently, the prevalent commonsense view of emotion, endorsed by many, was that emotions were disruptive to functioning, were due to misinterpretation and were to be controlled, tempered, bypassed, or avoided (Beck, 1976). Control of emotion, however, is not always wise or adaptive, and overregulation of emotion, or its avoidance, does not ensure health or happiness. A large volume of research has now been collected on the debilitating physiological effects of not expressing deeply felt emotions (Traue & Pennebaker, 1993). It appears that inhibiting the expression of emotion can lead to impaired immune system function and poorer health on a variety of indices. In addition, there is increasing evidence on the importance of emotion knowledge and emotional intelligence in enhancing social competence and healthy development (Mayer & Salovey, 1997). Emotions are a fundamentally adaptive resource because they involve a meaning system that informs people of the significance of events to their well-being, and they organise people for rapid adaptive action (Frijda, 1986; Izard, 1991; Oatley & Jenkins, 1992; Tomkins, 1963). From birth onward, emotion also is a primary signalling system that communicates intentions and regulates interaction (Sroufe, 1996). Emotion thus regulates self and other and gives life much of its meaning. With the advent of a view of emotion as an adaptive resource, the understanding of its relationship with cognition and its role in human functioning and psychotherapy has changed. This new look has begun to set a new agenda for psychological research-to determine the conditions under which emotions play a determining role in human experience and how this occurs. …