This article presents findings from the first year of a 3-year qualitative case study investigating teacher knowledge and voice in an ESOL curriculum development project. Participants were nine elementary ESOL teachers, a school district coordinator, and a university researcher. This study engages the strand of research on teacher learning and knowledge that investigates the role of social and institutional context in teacher learning. This context includes both concrete and sociocultural factors: from the number of students and available materials to the values and ideologies that inform policies and practices. Findings indicate that teachers' knowledge of context served as a critical mediator in curriculum development in three principal ways: establishing trust and gaining access, articulating and defining needs and concerns, and identifying and critiquing political factors that affect teachers' work. I argue that "contextualizing" is a form of teacher praxis, an articulation of the theory-practice dynamic in which teachers consider a range of intricate contextual factors as they work to develop a conceptual framework that will inform their work. These findings can help teacher educators and others understand the role of context in teachers' knowledge production. If teacher educators hope to help ESOL teacher learners succeed in their classrooms and learning communities, they must acknowledge the complexity of those communities and the factors that affect successful negotiation in them. (Contains 2 tables and 7 footnotes.)