The first island chain refers to the first chain of major Pacific archipelagos out from the East Asian continental mainland coast. It is principally composed of the Kuril Islands, the Japanese archipelago, the Ryukyu Islands, Taiwan (Formosa), the northern Philippines, and Borneo, hence extending all the way from the Kamchatka Peninsula in the northeast to the Malay Peninsula in the southwest. The first island chain forms one of three island chain doctrines within the island chain strategy in the U.S. foreign policy.

The East China Sea is a marginal sea of the Western Pacific Ocean, located directly offshore from East China. China names the body of water along its eastern coast as "East Sea" due to direction, the name of "East China Sea" is otherwise designated as a formal name by International Hydrographic Organization (IHO) and used internationally.