This article provides a context for understanding how social networks among teachers support or constrain school improvement in terms of instructional practice, professional development, and educational reform. It comments on the articles in this special issue, summarizing their contributions to the field. This analysis reveals several important lessons including the finding that teachers' social networks can be leveraged to work toward positive change, and yet teachers' social networks may also thwart change. Moreover, the architecture of teachers' social networks may change during the process of reform. Implications for further research are discussed.