This article describes why measurement invariance is a critical issue to quantitative theory building within the field of human resource development. Readers will learn what measurement invariance is and how to test for its presence using techniques that are accessible to applied researchers. Using data from a LibQUAL+[TM] study of user perceptions of service quality, we demonstrate how measurement invariance can threaten the validity of group comparison tests and ensuing theoretical conclusions. Moreover, we identify how measurement invariance can uncover important relationships in data that would otherwise go left unnoticed. (Contains 4 figures and 6 tables.)