The following describes research supported by the Teagle Foundation for the development and testing of an instrument for measuring college student perceptions of institutional mission in the learning environment. Findings from reliability and validity testing of a set of questions called the Mission Perception Inventory (MPI) are discussed. The MPI was first developed in 2004 from qualitative analysis of selected mission statements of postsecondary institutions in the United States. Questions were formulated around the construct of mission perception, operationally defined as an individual's judgment of his or her engagement in the learning environment of an institution as defined by its mission. Testing was performed on data from four consecutive annual administrations of the MPI appended as consortia questions to the National Survey of Student Engagement (NSSE). Data were obtained from a sample of men and women in the first and senior college years (N = 18,671). Results from reliability and factor analysis of the data support the construct validity and reliability of the scale by year in terms of stability, internal consistency, and item-total correlation matrices. This Professional File provides consistent evidence that the MPI is a valid and reliable measure over time in a changing student population. Hence, this instrument can be a useful outcomes measure for activity focused on advancing institutional mission on college campuses. (Contains 3 tables and 2 figures.)