Teacher collaboration has become an increasingly important lever for school improvement efforts. This is especially true in high need urban districts, which struggle with capacity building in the face of significant teacher turnover, major shifts in curriculum and instruction, and scarce resources. This paper employs a mixed methods approach to analyze the landscape of teacher networks in a sample of district and charter schools in Philadelphia. Hierarchical linear modeling, social network analysis, and qualitative analysis are used to evaluate the types and functions of networks, school and teacher characteristics associated with participation in networks, and the value teachers associate with networks. The findings support previous research on the role of networks in improving school climate, broadening teacher expertise, and increasing job satisfaction and persistence in the field. Policy and research recommendations are offered to districts and schools. The most effective