The overall aim of this thesis was to explore therapeutic action in psychoanalytic psychotherapy from different perspectives (patient, therapist, observer), using different methodological approaches (qualitative and quantitative). Study I explores patients’ views of therapeutic action with grounded theory methodology. The results indicated that talking openly in a safe therapeutic relationship led to new relational experiences and expanding self-awareness. Hindering factors included difficulties “opening up” and experiencing something missing in treatment. Study II investigates experienced therapists’ views of therapeutic action. The development of a close and trusting relationship was perceived as the core curative factor. Patients’ fear of closeness hindered treatment from the therapists’ perspective. Study III involves the development and psychometric examination of a new rating scale for patient-therapist attachment (Patient Attachment to Therapist Rating Scale; PAT-RS). Inter-rater reliability was good for three of the subscales (Security, Deactivation, Disorganization), but poor for one (Hyperactivation). Patterns of correlations with other measures suggest construct validity for the reliable subscales. Study IV examines the relationships between secure attachment to therapist, alliance, and outcome. Linear mixed-effects models, controlling for therapist effects, treatment length and patient-rated alliance, indicated that secure attachment to therapist relates to outcome. Further, the unique variance associated with secure attachment to therapist predicted continued gains in functioning during follow-up. The results of this thesis suggest that the development of a secure attachment to the therapist is a central mechanism of therapeutic change. The results are discussed in relation to established notions of therapeutic action in psychoanalytic psychotherapy. Two tentative process models that may be useful for clinical practice and future research are proposed.