We present a view that conceives of conceptual learning as changes in discourse practices. This view focuses on interactions in which people construct understanding collaboratively, either as deliberate conceptual inquiry or to facilitate accomplishing something else. Our analysis combines concepts and methods from ethnography (e.g., Jordan & Henderson, 1995), linguistic discourse analysis (e.g., Lemke, 1990), cognitive analyses of conceptual growth (e.g., Keil, 1994), and theories of information structures in comprehension and reasoning (e.g., Kintsch & van Dijk, 1978). In this view, conceptual understanding is considered mainly as an interactional process. The view focuses on how concepts are created and built up when people engage in activity, especially when they communicate about the things they are doing and trying to understand. Participation in a community includes using its concepts according to practices in which members communicate, coordinate their action, and achieve mutual understanding. Our view of concepts is illustrated with examples drawn from a study of two FCL science classes.