Many organizations operate multiple business models (BMs) concurrently. Yet, we know little about the challenges of managing a BM portfolio in one organization. In this study, we examine complexity as an important issue facing multi-BM firms. We differentiate complexity within a single BM from the complexity of links between BMs managed by a focal organization. Linking the BM and corporate strategy literatures, we discuss important dimensions and consequences of complexity in a BM portfolio. The sharing of similar activities and partners and the redeployment of activities and partners across BMs are important dimensions of the complexity of an integrated BM portfolio. We also suggest that BM portfolio complexity should be aligned with organizational design in terms of the centralization or decentralization of the decision-making process, and identify the positive effect of BM portfolio complexity on building imitation barriers.