Marine environmental conditions are very distinct in the Yellow Sea, the East China Sea, and the East/Japan Sea. Physico-chemical properties and subsequently biological characteristics are different among the three seas. During the recent decades, dramatic changes in physical structure and vertical distribution of chemical properties were reported in the Yellow Sea, the East China Sea, and the East/Japan Sea. However, we do not know much about the current status of the marine ecosystems in these three distinct seas to date. Since 2018, the integrated ecosystem assessment for ecosystem-based fisheries management have been implemented in the Yellow Sea, the East China Sea, and the East/Japan Sea by the National Institute of Fisheries Science, Korea. This special volume will provide basic information for the current status of the marine ecosystems and an important background for the future monitoring of marine ecosystem responses to ongoing climate changes in the Yellow Sea, the East China Sea, and the East/Japan Sea.