This field manual (FM) provides guidance to commanders, counterintelligence (CI) agents, and analysts. The first four chapters provide information to the commander and staff while the remainder provides the tactics, techniques, and procedures (TTP) required to aggressively identify, neutralize, and exploit foreign intelligence attempts to conduct operations against the United States (US) Army. CI supports Army operations by providing a clear picture of the threat to commands at all echelons and actions required to protect the force from exploitation by foreign intelligence. CI operations include conducting investigations, offensive and defensive operations, security and vulnerability analysis, and intelligence collection in peace and at all levels of conflict to support command needs. CI supports the total intelligence process by focusing on foreign intelligence collection efforts. CI is designed to provide commanders the enemy intelligence collection situation and targeting information in order to counter foreign intelligence service (FIS) activities. CI is an integral part of the US Army's all-source intelligence capability.