"Essays in CSCL" reports on the author's research in computer-supported collaborative learning, covering a broad range of topics. It begins with general reflections on the importance of CSCL as a research field, situating Stahl's work on the Virtual Math Teams Project and his theory of group cognition within the field of CSCL. It describes the VMT research project, including its research approach, technology, pedagogy and analysis methods. Mostly, it discusses in some detail the findings that have emerged from the VMT Project about the nature of online interaction in that type of CSCL setting. The volume concludes with reports of current work in the project and future directions that are underway. In this way, it elaborates, deepens and extends the presentation in Stahl's first two major publications, "Group Cognition" (2006, MIT Press) and "Studying Virtual Math Teams" (2009, Springer) and prepares the broader background for the companion volume, "Essays in Group Cognition" (2011, Lulu).