This article highlights key online teacher professional development (oTPD) areas in need of research based on a review of current oTPD research conducted in conjunction with an oTPD conference held at Harvard University in fall 2005. The literature review of this field documents much work that is anecdotal, describing professional development programs or "lessons learned" without providing full details of the participants, setting, research questions, methods of data collection, or analytic strategies. Until more rigorous oTPD research is conducted, developers are hard pressed to know the best design features to include, educators remain uninformed about which program will help support teacher change and student learning, and funders lack sufficient guidelines for where to direct their support. The authors believe that the recommendations in this article for a research agenda will guide oTPD scholarship toward an evidence-based conceptual framework that provides robust explanatory power for theory and model building. (Contains 2 figures.)