The Second United Front was the alliance between the ruling Kuomintang (KMT) and the Chinese Communist Party (CCP) to resist the Japanese invasion of China during the Second Sino-Japanese War, which suspended the Chinese Civil War from 1937 to 1945.

As a result of the truce between KMT and CCP, the Red Army was reorganized into the New Fourth Army and the 8th Route Army, which were placed under the command of the National Revolutionary Army. The CCP agreed to accept the leadership of Chiang Kai-shek, and began to receive some financial support from the central government run by KMT. In agreement with KMT Shaan-Gan-Ning Border Region and Jin-Cha-Ji Border Region were created. They were controlled by the CCP.

After the commencement of full-scale war between China and Japan, the Communists forces fought in alliance with the KMT forces during the Battle of Taiyuan, and the high point of their cooperation came in 1938 during the Battle of Wuhan.

However, the Communists submission to the chain of command of the National Revolutionary Army was in name only. The Communists acted independently and hardly ever engaged the Japanese in conventional battles. The level of actual coordination between the CCP and KMT during the Second Sino-Japanese War was minimal.