PurposeDrawing on institutionalism supplemented by a micro-political perspective, this study explores how a bilateral development agency’s (BDA’s) regional office manages institutional multiplicity, a situation where organisations are embedded into the institutional environments of their headquarters and multiple host countries.Design/methodology/approachI remotely conducted semi-structured in-depth interviews with 20 staff members of a BDA’s regional office in South-East Europe. Reflexive Thematic Analysis was used to analyse the interview data.FindingsTwo themes are developed. One is an institutional decomposition strategy. The subject office decomposes institutional multiplicity into more manageable multiple institutional dualities by deploying local representatives to host countries. The other is the division of duties to demonstrate legitimacy. The division designates who in the office demonstrate legitimacy in which institutional environment. These proactive actions by the office (i.e., the decomposition and the division) question the institutionalist assertion that external institutional conditions determine organisational behaviour.Research limitations/implicationsThe findings may not directly apply to other public sector organisations because BDAs’ overseas offices are “donors” for their host countries. In addition, themes developed in the context of South-East Europe may not be generalisable to other regions.Practical implicationsBDA staff members should understand that institutional decomposition through the deployment of local representatives is a rational strategy to deal with complex conditions of institutional multiplicity. They should also understand that experienced local representatives are required to achieve this strategy.Originality/valueThis is the first empirical study to examine how a public sector organisation’s regional office manages complex institutional multiplicity from a micro-macro combined perspective.