Theorists have highlighted the commonalities in cognitive and behavioural processes across multiple disorders i.e. transdiagnostic approach. We report two studies that tested the psychometric properties of a new scale to assess these processes. The Cognitive and Behavioural Processes Questionnaire (CBP-Q) was developed as a 15-item measure. In Study 1, the CBP-Q was administered to a student (n = 172) sample with a range of standardised measures of the processes and symptom measures. Study 2 repeated the evaluation in a mixed clinical group (n = 161) and a community control group (n = 57). An exploratory factor analysis resulted in a 12-item version of the CBP-Q, consisting of a single factor. The measure demonstrated good internal consistency, testretest stability and satisfactory convergent and divergent validity in both studies. Correlations with symptom-based measures showed increased engagement in these cognitive and behavioural processes to be associated with higher levels of symptomatology. The scale was elevated in the clinical relative to the community group and there were no differences in scores between broad diagnostic groupings (anxiety vs. mood vs. other). The CBP-Q has good psychometric properties. The findings are consistent with the transdiagnostic approach and indicate that a single, as yet unspecified factor may account for the shared variance across cognitive and behavioural maintenance processes.