In developing the Online Self-regulated Learning Questionnaire (OSLQ) to address the need for an instrument measuring self-regulation in the online learning environment, this study provides evidence toward the reliability and validity of the instrument. Data were collected from two samples of students. The first sample of students took coursework using an online course format while a second sample of students took coursework delivered via a blended or hybrid course format. Cronbach alpha ([alpha]) and confirmatory factor analyses were performed to assess the psychometric properties of the OSLQ across both samples of students. Results indicate the OSLQ is an acceptable measure of self-regulation in the online and blended learning environments. (Contains 3 figures and 4 tables.)