Taking broadly sociocultural or sociolinguistic perspectives, the five contributions to this special issue investigate various aspects of the co-construction of knowledge, as this is manifested in K-16 classrooms in Canada, the United Kingdom, and the United States. While the authors of these papers address different educational settings, student populations, and curricular content, what unites them is their concern to better understand the cumulative, multidimensional nature of learning and teaching and the ways in which this is enacted in action and discourse across different spaces and over different scales of time.