Cognitive behavioural therapy (CBT) is an empirically grounded approach which typically relies on formulation to guide the shape and course of therapy. Cognitive formulation is widely advocated but poorly understood at an empirical level. This study aimed to characterize how clinicians understand the structure and uses of formulation and how they report on using it in their clinical practice relative to an expert reference group. A total of 124 clinicians in routine clinical practice completed a questionnaire, which assessed their clinical use and understanding of formulation. For some aspects of the questionnaire a comparison with a reference group, 15 highly specialist CBT therapists, was used. High levels of self-rated expertise were noted and at levels comparable to that of the highly specialist group. Participants rated themselves as less capable in terms of their formulation skills relative to their self-rating in CBT overall. Formulation is typically rated as important by those with some professional commitment to CBT. There may be some gaps in the way formulation is applied in clinical practice that should be addressed at the level of training and supervision.