Assumptive World Theory (Janoff-Bulman, 1992) proposes that traumatic events are psychologically distressing because they shatter some of survivors’ fundamental assumptions about the world. This idea has been regarded as a truism in the trauma literature, although tests of the theory have provided mixed results. More recently, reviews of the most commonly used measure of the assumptive world, the World Assumptions Scale (WAS; Janoff-Bulman, 1989), have revealed flaws in its psychometric properties. Thus, the current study aims to develop a new measure of the assumptive world, the World Assumptions Questionnaire. Qualitative survey and interview data were collected from trauma survivors, undergraduates, trauma researchers, and clinicians treating trauma survivors to generate content domains and items. An initial quantitative survey study of 236 undergraduates was used to evaluate the underlying factor structure of the item pool and select items for the final scale. A second quantitative, repeat-administration, survey study of 312 undergraduates yielded findings that the World Assumptions Questionnaire had strong psychometric properties including satisfactory temporal stability, a stable factor structure reflective of the proposed measurement model, satisfactory internal consistency reliability, and more evidence of content and construct validity. Results from these studies are presented and implications for further research are discussed.