In this chapter I address what I see as the cornerstone for advancing our understanding of how results from empirical research into L2 interactional development can usefully be brought to bear on L2 education--be it curriculum design, teaching or testing--, namely an epistemologically coherent understanding of interactional competence and its development. For this purpose, I outline how current thinking about interactional competence--and more generally about L2 development--is rooted in a socio-constructivist, dialogic ontology of language, learning and competence as fundamentally situated, distributed, and emerging in and through social interaction. I discuss how this conceptualization differs from the notion of communicative competence, and argue that it stands in sharp contrast to the individualistic and cognitivist approaches to SLA that represent the epistemological backbone of L2 education in many contexts. Most centrally, I examine how existing findings from recent longitudinal studies on the development of L2 interactional competence can help us understand the challenges and the affordances of L2 classroom interaction, and I conclude with some larger implications for L2 education. [For the complete volume, "Classroom-Based Conversation Analytic Research: Theoretical and Applied Perspectives on Pedagogy. Educational Linguistics. Volume 46," see ED660574.]