Modern multiuser software systems have adopted Role- Based Access Control (RBAC) for authorization management. This paper presents a formal model for RBAC policy validation and a static-analysis model for RBAC systems that can be used to (i) identify the roles required by users to execute an enterprise application, (ii) detect potential inconsistencies caused by principal-delegation policies, which are used to override a user?s role assignment, (iii) report if the roles assigned to a user by a given policy are redundant or insufficient, and (iv) report vulnerabilities that can result from unchecked intra-component accesses. The algorithms described in this paper have been implemented as part of IBM?s Enterprise Security Policy Evaluator (ESPE) tool. Experimental results show that the tool found numerous policy flaws, including ten previously unknown flaws from two production-level applications, with no false-positive reports.