The main purposes of this article are to study the normative characteristics of the Operational Policies and Procedures (OPPs) upon which the World Bank Inspection Panel (IP) bases its decisions, and to examine whether and how the IP has contributed to ‘hardening’ the legal characteristics of the Bank's OPPs. The latter task involves a critical examination of the view that the IP is to be regarded as a bottom-up accountability instrument essentially internal to the World Bank. My main underlying hypothesis is that the OPPs in combination with the IP have contributed to ‘harden’ the ‘soft’ characteristics of the World Bank. Such a process of hardening ‘soft law’ can be termed a process of ‘legalization’.