Massive open online courses (MOOCs) offer opportunities for professional development of environmental educators globally, yet we lack understanding of participants™ cognitive and social learning processes and of how instructors can enhance these processes. Based on the Community of Inquiry framework, we used a survey and coded participant discussion board and Facebook posts to examine the cognitive, social, and teaching presence in the Environmental Education: Transdisciplinary Approaches to Addressing Wicked Problems MOOC, offered by Cornell University. Rather than train educators in a specific curriculum, the goal of the MOOC is to expand educators™ critical and transdisciplinary thinking about the field of environmental education and to enhance social interactions to support learning, educators, and knowledge co-creation. Results indicate that cognitive presence is higher on the discussion board whereas social presence is higher on Facebook. Over half of cognitive posts focused on exploration, a lower level of learning, whereas just less than a fifth reflected higher level integration, suggesting room for enhancing cognitive learning. Our results suggest strategies to encourage higher levels of thinking and more meaningful social interactions to foster learning, educator support, and co-creation of knowledge, thereby improving online professional development.