Historically, studies of Group Decision Support (GDS) have focused on assessing the degree to which using a GDS makes groups more effective, typically via carefully designed experiments and case study reports. More recently, we have witnessed a growing interest in getting close to GDS practitioners to see how their work is actually done in "real time,'' "there-and-then.'' What motivates this interest is the recognition that in order to develop better GDS practice we must first pay attention to how it is actually used by those involved in situ. By zooming in on what GDS practitioners actually do with their craft, and the critical role of these doings on generating group outputs and outcomes, a more nuanced understanding of GDS practice can be achieved. Furthermore, this understanding can inform the development of more effective GDS practitioner training and teaching materials. In this chapter we introduce a particular way of studying GDS practice, "as it happens'' on the ground, based on ethnomethodology (EM). To illustrate the approach, we provide an example of its application to study GDS practice in a facilitated, computer-supported causal mapping workshop. Overall, the analysis reveals the various ways in which actual GDS practice is accomplished over time, as it happens on the ground, and with what effects. We conclude the chapter by summarizing the distinctive contribution that an ethnomethodologically informed perspective makes to GDS theory and practice, and outlining some potentially useful avenues for future research.