Online courses play an increasing role in professional development of environmental educators, yet little information is available on the interactive processes involved in online learning. We examined the relationship of three types of interactions in an urban environmental education online course -participantparticipant, participant-instructor, and participant-content -to four course outcomes: participants' motivation to learn, intent to adapt ideas and information learned through the course in their practice, actual adaptation of ideas in their practice, and development of professional networks. Content analysis was used to characterize participants' and instructors' weekly online posts and comments, and generalized estimation equation modeling was used to explore the relationships between interactions and outcomes. The results showed that participant-content interaction had significant positive relationships with participants' motivation to learn, intent to adapt ideas, and adaptation of ideas. Participantparticipant interaction had significant positive relationships with participants' motivation to learn, and development of professional networks with each other. Finally, participant-instructor interaction had a significant positive relationship with participants' development of professional networks. The results of this study can be used to improve professional development online courses for environmental educators.Keywords: environmental education; online learning; professional development; interactive learning; professional networks Introduction As online courses become increasingly popular, course designers are searching for ways to create learning experiences that move beyond content acquisition to incorporate meaningful interactions among learners and between learners and instructors (cf. Alexander, Schallert, and Reynolds 2009;Illeris 2007;Sfard 1998). Interactive theories of learning would support such experiences, including theories focusing on how students construct knowledge through processes of assimilation and accommodation (Piaget 1952) and how participants move from an inexperienced to skilled member of a community of practice (Lave and Wenger 1991;Rogoff et al. 2003;Wenger, McDermott, and Snyder 2002). Related theories focus on the social, cultural, and historical contexts of learning (Lemke 2001), and on the importance of reciprocal interactions among learners' behaviors, capabilities, and surrounding environment (Bandura 1977 (Dillard 2006). The evaluation of the national environmental education program Project Learning Tree's online workshop found that participants were motivated to use learned activities in their practices (McConnell and Monroe 2012). Fleming and Easton (2010) point out challenges in teaching online courses for environmental educators, including attrition rates and creating a social learning environment. Studies of online courses focused on environmental issues rather than environmental education per se have demonstrated that participants not only increased environmental k...