This study investigated how three instructors developed their professional learning of beliefs, knowledge, and practice by examining their professional learning processes using constructive, social constructive, and transformative theoretical perspectives on learning. It also focused on their challenges and supports in developing their professional learning. This case study selected three instructors who are teaching online professional development courses at a Mid-western university, by using purposeful and convenience sampling strategies. Data included pre- and post interviews, three written reflections, and online instruction observations. The findings show that the three instructors developed their beliefs, knowledge, and practice about online teaching by using their own professional learning opportunities, such as reflecting on their online teaching and learning experiences, discussing with experienced instructors and their colleagues, doing self-study, and participating in workshops and seminars. The three instructors solidified their beliefs by implementing their values in effective online instruction, building up their pedagogical, content, and technological knowledge, and challenging and transforming their practices. The study also shows that the three instructors experienced challenges in developing their beliefs, knowledge, and practice because of external and internal barriers. Regarding the external barriers, the three instructors wanted online teaching preparation (training or taking online classes), ongoing support (providing online or face-to-face professional development opportunities), having discussion opportunities (with mentors and with colleagues or experienced instructors), access to resources and self-paced learning opportunities, and department support (reducing time or technology support). Regarding the internal barriers, the three instructors showed that they needed to change their negative thoughts or concerns about teaching online; they needed to transition to online culture (emphasizing email communication, asynchronous/synchronous discussion, online etiquette, and collaboration and social interaction); and they needed to have flexible and adaptable attitudes about their teaching. The implications for practice and research of online professional development are discussed. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]