In the wake of new forms of curricular policy in many parts of the world, teachers are increasingly required to act as agents of change. And yet, teacher agency is under-theorised and often misconstrued in the educational change literature, wherein agency and change are seen as synonymous and positive. This article addresses the issue of teacher agency in the context of an empirical study of curriculum making in schooling. Drawing upon the existing literature, we outline an ecological view of agency. These insights frame the analysis of a set of empirical data, derived from a research project about curriculum making in a school and further education college in Scotland. Based upon the evidence, we argue that the extent to which teachers are able to achieve agency varies from context to context based upon certain environmental conditions of possibility and constraint, and that an important factor in this lies in the beliefs, values and attributes that teachers mobilise in relation to particular situations.