Recent theories of obsessive-compulsive disorder (OCD) emphasize the importance of cognitive contents (beliefs and appraisals) and cognitive processes in the etiology and maintenance of OCD. In order to evaluate these theories and to assess the mechanisms of treatment-related change, it is necessary to develop measures of the relevant cognitive contents and processes. Several scales have been developed, although many are unpublished and there is a great deal of overlap among measures. The purpose of the present article is to describe the progress of an international group of investigators who have commenced a coordinated effort to develop a standardized set of cognitive measures. This article describes the theoretical bases and clinical importance of such an endeavor, and the proceedings of the working group meetings are summarized. Several methods of assessment are reviewed, including idiographic methods, information processing paradigms, and self-report measures. The working group is currently developing and evaluating self-report measures of appraisals about intrusions, and self-report measures of OC-related beliefs. Consensus ratings indicated that 6 belief domains are likely to be important in OCD. These are beliefs pertaining to: (1) inflated responsibility; (2) overimportance of thoughts; (3) excessive concern about the importance of controlling one's thoughts; (4) overestimation of threat; (5) intolerance of uncertainty; and (6) perfectionism.