This paper reports on research into how a systems development methodology (SDM) operates as an institution: specifically – an institutional carrier in the process of systems development. The case study develops the argument that institutional structures (such as authority, norms, symbolic values, and routine ways of doing things) embedded within the methodology are active forces in the systems development process, and therefore constitutes ‘institution’. We ground our argument on the findings from a study of an in-house developed SDM in a large IT department within a major bank in Australia. The findings show how the SDM exerts its influence in the bank through a combination of shared regulative, normative, and cultural-cognitive elements. As a second contribution to research, the study operationalises a framework derived from new institutional theory that integrates elements of a social actor model outside its original domain to provide a deeper understanding of the institutional forces at play in information systems development. All these findings are significant in that they draw attention to the role of institutional carriers, control structures, conflicting interests, and power that appear largely outside the domain of the systems developer.