The State Security Service (SSS), self-styled as the Department of State Services (DSS), is a security agency in Nigeria and one of three successor organisations to the National Security Organization (NSO). The agency is under the Presidency of Nigeria, and it reports its activities direct to the President, office of the ONSA, headquartered in Abuja.

A security agency is a governmental organization that conducts intelligence activities for the internal security of a nation. They are the domestic cousins of foreign intelligence agencies, and typically conduct counterintelligence to thwart other countries' foreign intelligence efforts.