We describe the development of the Electronic Prescription Service (EPS), the solution for the electronic transmission of prescriptions adopted by the English NHS for primary care. The chapter is based on both an analysis of data collected as part of a nationally commissioned evaluation of EPS, and on reports of contemporary developments in the service. Drawing on the notion of an installed infrastructural base, we illustrate how EPS has been assembled within a rich institutional and organizational context including causal pasts, contemporary practices and policy visions. This process of assembly is traced using three perspectives; as the realization and negotiation of constraints found in the wider NHS context, as a response to inertia arising from limited resources and weak incentive structures, and as a purposive fidelity to the existing institutional cultures of the NHS. The chapter concludes by reflecting on the significance of this analysis for notions of an installed base.
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