Multilateral development banks (MDBs) have proved to be one of the most popular and enduring forms of international organization ever created, in large part because of their unique financial model. MDBs raise most of the resources needed for operations from international capital markets rather than government budgets, which greatly increases their financial capacity and attractiveness to member governments. However, this model has a trade-off: MDBs must pay close attention to the perceptions of bond investors, who have little interest in development goals. This paper explores the influence of credit rating agencies (CRAs) on MDB operations, based on an analysis of the methodologies used by CRAs to evaluate MDBs and interviews with MDB financial staff and CRA analysts. The study demonstrates that the methodology used by Standard and Poor’s seriously undervalues the financial strength of MDBs, limiting their ability to pursue their development mandate. These findings suggest that MDB dependence on capital market financing may weaken the ability of major shareholder governments to fully control MDB activities.