Inga-Britt Monica Stigsdotter Ahlenius is a Swedish auditor, public servant and former Under-Secretary-General for the United Nations Office of Internal Oversight Services (OIOS).

The United Nations Office of Internal Oversight Services (OIOS) is an independent office in the United Nations Secretariat whose mandate is to "assist the Secretary-General in fulfilling his internal oversight responsibilities in respect of the resources and staff of the Organization." Specifically, activities include internal audit, investigation, monitoring, evaluation, inspection, reporting and support services to the United Nations Secretariat.