The American and Filipino guerrillas that fought against the Japanese occupation of the Philippines were key in providing direction to resistance efforts and in the eventual liberation of the islands. The guerrillas escaped the aggressive counter-guerrilla efforts of the Imperial Japanese Army. The Japanese failure to deal with isolated soldiers and civilians provided the time they needed to organize into guerrilla groups and prepare for American forces liberation of the Philippines. This analysis of American and Filipino insurgents covers the effectiveness of Japanese counter guerrilla efforts, the intelligence structure created by General Douglas MacArthur's staff to support the guerrillas, the guerrilla's contributions to the liberation of the Philippines, and it examines how Americans would form guerrilla groups and fight as insurgents behind enemy lines if circumstances warranted. Additionally, it provides general insight as to how resistance movements form.