As recounted in one of the opening chapters (diSessa, Sherin, & Levin), the current volume has its roots in Andy diSessa’s long-standing project to document the development of students’ conceptual understandings of physical principles (e.g., diSessa, 1983, 1991, 1993). His approach to studying these matters, what he terms Knowledge Analysis (KA), employs methods appropriate to the fine-grained analysis of interaction. Whereas studies of cognition and studies of interaction are often viewed as disjunct, even oppositional, enterprises, diSessa, in his work, has ambitiously attempted to bridge these two programs. The discussions that eventually led to the production of this volume were undertaken to sort out some of the issues related to this marriage, that is to sort out “the relationship between knowing and interacting” (Enyedy & Danish, commenting on Sherin, this volume, p. 448). This began with an AERA-sponsored workshop that occurred in 2011. Later came two symposia, one at AERA in 2012 and another at ICLS in 2014. Along the way, a number of new voices have joined the conversation, producing the rich collection of contributions that comprise this volume.