Sixty-five expert, experienced, and novice cognitive-behavioral and psychodynamic psychotherapists provided "think aloud" case formulations in response to 6 standardized patient vignettes varying in disorder and prototypicality. The 390 formulations were reliably transcribed, segmented into idea units, content coded, and rated on multiple dimensions of quality. As hypothesized, the formulations of experts were more comprehensive, elaborated, complex, and systematic. Judges did not rate them as more coherent or precise in the use of language. In addition, the treatment plans of experts were more elaborated and linked better to the formulations. Effect sizes for overall ratings of quality ranged from medium to large. Few differences based on therapy orientation were observed. Results are discussed in terms of therapist training.