The introductory psychology course is offered by nearly all undergraduate psychology programs. Given its prominence in curricula, there have been calls to develop reliable and valid assessments of introductory psychology knowledge to inform and evaluate instruction. The current research, guided by the American Psychological Association's five content pillars model for the introductory course, developed and evaluated a relatively brief inventory that can be easily administered and scored to assess students' knowledge of introductory psychology. We followed established test development guidelines to write and revise inventory items. Then, we conducted two evaluation studies in which we administered the inventory to introductory psychology courses at two higher education institutions and to a sample of US adults to assess the reliability and validity of the test. Results suggested that the inventory has convergent (high correlations with course exam scores, all ps Ͻ .001), discriminant (low correlations with ACT English and Reading scores, all ps Ͻ .05), and known-groups validity (students that had taken high school psychology scored higher, all ps Ͻ .001). The inventory also demonstrated adequate test-retest reliability across a 1-week time interval, r ϭ .80, p Ͻ .001. In a third study, we surveyed introductory psychology instructors about the inventory. The majority (97.4%) reported that it was representative of typical course content, and 75.7% reported they would use the inventory. We conclude that this introductory psychology knowledge inventory offers a practical, useful, reliable, and valid means of assessing students' knowledge and learning in the introductory course.