The Cognitive Mediation Beliefs Questionnaire is a 15-item tool that assesses individuals' emotion beliefs about the cognitive mediation of emotions. It measures two emotion beliefs: stimulus-response generation beliefs and cognitive mediation change beliefs. This study aimed to reduce the number of items and test the validity of a briefer version of the Cognitive Mediation Beliefs Questionnaire. We combined data from 13 unpublished data sets collected between 2019 and 2023 and reached a final sample of 2,872 participants. While this data set is relatively large and diverse (e.g., participants from 53 nationalities), most were from developed countries, and the data were not fully representative across demographic characteristics, such as age and ethnicity. The data were randomly split by 50%/25%/25% (60%/40% female/male) to conduct one exploratory factor analysis and two confirmatory factor analyses. Using an iterative process in the exploratory factor analysis, seven items were deleted for failing to meet item retention criteria, resulting in an eight-item solution across two factors. Across two confirmatory factor analyses with independent samples, the eight-item and the 15-item solutions were tested. The eight-item model was superior in terms of model fit in both samples. These results were in line with our hypothesis in that an eight-item Short Cognitive Mediation Beliefs Questionnaire confirmed the validity of the two-factor structure. The present study offers a valid and efficient measure of emotion beliefs that can be used to make a rapid assessment of beliefs about emotions and to support clinical interventions, particularly cognitive behavioral therapy approaches, where cognitive change is fundamental. (PsycInfo Database Record (c) 2024 APA, all rights reserved).