For more than a decade, scholars and practitioners have noted the disconnection between E&C and CSR practices in US corporations and called for their alignment. There is scant literature on why this lack of alignment persists. This article applies communities of practice theory to illuminate the separate learning trajectories that the E&C and CSR fields in the US have taken over the past twenty five years, anchored by their respective professional associations. This article provides an important perspective on the role that n, boundaries, ethics and compliance, corporate social responsibility communities of practice play in reifying the knowledge and competencies within E&C and CSR, and the boundaries to collaboration that exist between their managers and practices. It also calls attention to the fact that alignment is not the only alternate trajectory that these practices and their communities may take in the future, and five distinct evolutionary paths are explored.