The authors describe the development and psychometric properties of a new measure called the Skills of Cognitive Therapy (SoCT) in depressed adults and their cognitive therapists. The 8-item SoCT assesses patients' understanding and use of basic cognitive therapy (CT) skills rated from the perspectives of both observers (SoCT-O; therapists in this report) and patients (SoCT-P). Ratings of patients' skill usage are made on 5-point Likert-type scales ranging from 1 ("never") to 5 ("always or when needed"). Higher scores reflect greater patient skill in applying cognitive therapy principles and coping strategies. To develop this scale, a 33-item pool was used, rated by both patients and their therapists at the middle and end of CT (Ns = 359-416), and evaluated the reliability and concurrent and predictive validity of both versions of the scale. The SoCT has excellent internal consistency reliability and moderate correlations between the observer and patient versions. It is important to note that the SoCT showed good predictive validity for response when collected at the midpoint of acute phase CT. Considering both patients' self-ratings and clinicians' SoCT ratings, the odds ratio for responding to CT was 2.6. The practical utility of the SoCT is discussed, as well as its theoretical importance in research of patient CT skills (e.g., acquisition, comprehension, and generalization) as putative moderators or mechanisms of symptom change in the therapy. (Contains 6 tables and 2 footnotes.)