Aberrant salience is the unusual or incorrect assignment of salience, significance, or importance to otherwise innocuous stimuli and has been hypothesized to be important for psychosis and psychotic disorders such as schizophrenia. Despite the importance of this concept in psychosis research, no questionnaire measures are available to assess aberrant salience. The current research describes 4 studies designed to develop and validate the Aberrant Salience Inventory (ASI) as a measure of aberrant salience. In Study 1, an overinclusive item pool was subjected to an exploratory factor analysis, and items were kept or discarded based on factor loadings. In Study 2, the 5-factor structure of the ASI was confirmed with a confirmatory factor analysis, and a 2nd-order factor analysis found evidence consistent with a single higher order factor. Study 2 also provided support for the scale score's convergent validity as the ASI was strongly associated with psychosis-proneness measures and dissociation measures and moderately correlated with measures associated with levels of dopamine. This study also provided support for its discriminant validity as the ASI was only weakly associated with social anhedonia. Study 3 found that participants with elevated psychosis proneness had increased ASI scores, but in contrast, participants with elevated social anhedonia had similar scores to comparison participants. Finally, Study 4 found that participants with a history of psychosis had elevated ASI scores compared to a psychiatric comparison group. Overall, the ASI demonstrated sound psychometric properties and may be useful for measuring aberrant salience and psychosis proneness in clinical and nonclinical samples.