Although several theories exist to describe why patients improve in cognitive-behavioral therapy (CBT), in only a limited number of studies has CBT skill acquisition been examined, particularly among patients with complex clinical profiles. Thus, the overarching aim of this research was to develop a tool to measure patients' use of CBT skills, such that it would have clinical utility for patients and therapists during treatment. In Study 1, the authors developed an initial set of items for the Cognitive-Behavioral Therapy Skills Questionnaire (CBTSQ). They submitted these items to an exploratory factor analysis in an initial administration (n = 350) and to a confirmatory factor analysis in a second administration (n = 378). Results indicated that there were two factors (Behavioral Activation and Cognitive Restructuring) with good factor structure and internal consistency, and both the factors evidenced expected relationships with other constructs. In Study 2, the criterion validity of the CBTSQ was investigated on a patient sample in a CBT-oriented treatment setting. Results showed that CBTSQ scores increased following treatment, and Cognitive Restructuring and Behavioral Activation scores predicted reduction of overall psychiatric symptoms and depression. Thus, the CBTSQ appears to be a promising measure of CBT skill acquisition and treatment outcome as well as an instrument that can help patients and therapists monitor progress specifically related to a CBT skills training treatment approach.