Counterintelligence is the knowledge needed for the protection and preservation of the military, economic, political, and socio- cultural strength and values of the state, including the security of the government in domestic and foreign affairs against or from espionage, sabotage and all other clandestine activities designed and aimed at the independence, territorial integrity and sovereignty of the state through the infiltration of foreign agents. Counterintelligence is adopted by the intelligence architecture of state as a supportive and complimentary measure of their primary mission of intelligence collection and analysis to ensure the protection of the state secret from espionage by hostile or unfriendly or even friendly foreign powers. The main purpose or essence of counterintelligence is to uncover and thwart foreign intelligence missions against the state. To this end, Specialists of counterintelligence waged a secret war against antagonistic or unfriendly intelligence service and terrorist organisations. This paper is an analysis of the concept, concerns, goals and challenges of counterintelligence. Using the analytical method and relying mostly on secondary sources, the paper argues that the first responsibility of counterintelligence is to protect classified information that are critical to the national security of the state, ensure physical security which involves keeping secret from all except those who need to be aware of it and providing personnel security which involves making sure that the people who are made aware of the state secrets protect those secrets responsibly. The paper in its findings submit that counterintelligence can be seen in three major perspectives – counterintelligence as a product, counterintelligence as an activity and counterintelligence as an organization.