This thesis describes a quasi-experimental study exploring psychotherapeutic process and outcome in 25 young adults sequentially assigned to psychoanalysis (n=14) or psychodynamic psychotherapy (n=11) at the Anna Freud Centre in London, England. Analysts reported process using a novel 899-item questionnaire, the Young Adult Weekly Rating Scale (YAWRS). Patients were assessed by an independent psychiatrist at intake, termination, and at 18 month intervals after intake and termination with Main and Goldwyn's Adult Attachment Interview (AAI) and on a host of symptomatic and diagnostic measures. The patients suffered from depression, anxiety, and personality disorders. Over the course of treatment (6 months to 8 years long), 12 of 19 patients (with adequate data) improved symptomatically on an aggregate measure. Ten of 12 improvers were in the psychoanalysis group, suggesting that it is a more effective treatment in this population. Data from 1,314 YAWRS questionnaires were factor analysed and used to test hypotheses from the psychotherapy process literature. In the first year of psychoanalysis (as compared with psychodynamic psychotherapy), higher scores on therapist dynamic technique, patient dynamic material, and negative patient transference were found. In the combined sample, higher scores in the first year on therapist dynamic technique, patient dynamic material, and discussion of contract were predictive of positive outcome. The AAI classifies patients according to security of "state of mind with respect to attachment" from narratives about early life relationship experiences. Our results show a high proportion of secure classifications at initial assessment and, in successful treatments, a movement towards a preoccupied-entangled attachment pattern which began to resolve by termination. We propose that the AAI be used to measure both structural health and regression/transference neurosis, which must occur and then resolve for treatment to succeed. Further research using the YAWRS and AAI is proposed.