Active Directory Membership Auditor is a Windows-based audit tool designed to enumerate and audit Active Directory (AD) security group memberships. It was developed by a former Microsoft Program Manager for Active Directory Security. The tool automates the enumeration of AD security group memberships, handling both direct and nested group structures, including detection of circular group nesting to prevent infinite loops. It supports auditing from two directions: enumerating all members of a given security group, or enumerating all groups to which a specific user account belongs. Results can be exported to CSV and compiled into customizable, professional-grade PDF audit reports. The tool operates in real-time against live AD environments and does not require administrative privileges, agent installation, or changes to the AD environment to function. It is licensed on a subscription basis (monthly, quarterly, or annual) and runs on any Windows computer. A free downloadable version is also available. Key use cases include access provisioning review, security compliance documentation, privileged group membership auditing (e.g., Domain Admins), and demonstrating regulatory compliance through archived audit reports.