Drawing from the positive psychology literature, the Inventory of Therapist Work with Strengths and Assets (IT-WAS) was constructed to measure the degree to which clinicians incorporate strength-based approaches in their therapy work. Two different samples were gathered in the current study; a professional sample (n = 128) and a university sample (n = 97). The professional sample was randomly selected from the 2005 membership directory of Divisions 17 (Counseling Psychology), 29 (Psychotherapy), and 42 (Independent Practice) of the American Psychological Association (APA), and resulted in a 51% return rate. The university sample consisted of graduate students in counseling related fields as well as faculty and counseling center staff at a large Mid-Atlantic university; the return rate for this sample was 62%. T-test results found no significant differences between samples on IT-WAS scores, and thus samples were combined for analyses. Three factors (Theory of Intervention, Strength Assessment, & Supporting Progress) were extracted by factor analysis, accounting for 52% of the total variance. The IT-WAS demonstrated very good internal consistency (α = .96) and test-retest reliability (r = .83). Scale validity was supported by positive associations between the IT-WAS and measures of favorable attitudes toward human nature, benevolent world assumptions, as well as therapist work with the strengths of a most recent client. Most therapists generally conducted strength-based clinical work to a high degree, supporting propositions made by Seligman (2002; Seligman & Peterson, 2003). Cognitive-behavioral, humanistic, multicultural, and feminist theoretical orientations were positively related to the IT-WAS, while psychodynamic and psychoanalytic theoretical orientations were negatively correlated to the IT-WAS. No differences between clinical and counseling psychologists were found on IT-WAS scores. Implications of therapist work with client strengths are discussed and areas for future research are provided.