The therapeutic alliance is considered an important mechanism of change in youth psychotherapy. Yet, alliance research with young people is scarce and hampered by methodological limitations. This PhD aimed to seek a deep understanding of the alliance and its role in psychotherapy for adolescent depression. Study 1 aimed to learn more about the empirical definition of the alliance and examined the factor structure of the most used alliance measure, the Working Alliance Inventory short-form. The theorised multidimensional structure was not supported, and a single, overall alliance dimension was found to be empirically more valid. Study 2 investigated whether the mean strength of the alliance, as well as its trajectory over time, differed between three equally effective psychological treatments for adolescent depression. The average alliance strength was found to differ across treatment types, being highest in cognitive therapy and lower in brief psychosocial intervention and especially psychoanalytic psychotherapy. Study 3 aimed to better understand the direction of the effect between alliance and outcome by investigating the associations between early alliance and subsequent outcome, while controlling for patients’ baseline severity and prior symptom change. It also examined potential moderators of this association. Early alliance was found to predict subsequent outcomes even after controlling for patients’ baseline severity and prior symptom change. The strength of this relationship was moderated by treatment type. Study 4 described and explored alliance rupture and resolution events and their impact on the change process in a single-case of a successful short-term psychoanalytic-psychotherapy. Frequent alliance ruptures occurred, but most of them were repaired. There was converging evidence that the patient-therapist relationship and its dynamics played a crucial role in promoting change. Together, these studies provide a rich picture of the role of the alliance in youth psychotherapy while challenging some of the assumptions in the current alliance literature
