This groundbreaking work, Undergrounds in Insurgent, Revolutionary, and Resistance Warfare, was written in response to the communist insurgency in South Vietnam. It sought to categorize underground movements encountered during the previous 30 years in fine detail so that the establishment and operations of subsequent underground arms of guerrilla forces railed against Free World Forces could be anticipated, located and disrupted or destroyed. Its secondary aim was to doctinalize tactics, techniques and procedures for the establishment of underground organizations in any given country in support of US Special Forces or Intelligence Community operations. One of the most important, and yet least known aspects of unconventional warfare is the underground. An underground is a clandestine arm of the unconventional warfare organization which sits out of sight of the general public and strives to remain as invisible to enemy security forces for as long as possible. For every guerrilla fighter, this report surmises that there are a minimum of seven underground operatives working to support the guerrilla's mission through providing logistics, communications, recruitment, intelligence, safe havens, medical support or covert operations. Conflict Research Group is proud to bring this book back into print as it should form a keystone of the research library of any practitioner or scholar in the unconventional warfare or security policy fields.