Recent developments force companies to rethink their value creation model and open themselves to other companies, which results in a shift from the traditional matrix or functional design to a more modular organization design. For example, even traditional banks open themselves and allow the ser-vices of specialized companies, to be integrated into their organization. Through this modular design, it is very easily possible to do it the other way around and conduct the outsourcing of certain business processes. The question that arises from this is whether and how the modularity of a firm’s architecture, consisting amongst others of the modularity of its business processes and its underlying IT support infrastructure, influences the incentive to outsource certain business processes. As a research-in-pro-gress paper, this manuscript develops a model of the multidimensional concept of modularity and links it causally to the determinants of a selective business process outsourcing (BPO) decision.