日本海是西北太平洋最大的边缘海，其东部的边界由北起为库页岛、日本列岛的北海道、本州和九州；西边的边界是欧亚大陆的俄罗斯；南部的边界是朝鲜半岛，其中韩国基于地理位置称其为东海，朝鲜则称为朝鲜东海，中国历史上称其为鲸海。日本海的水域有六个海峡与外水域相通，分别为：鞑靼海峡、宗谷海峡、津轻海峡、关门海峡、对马海峡和朝鲜海峡。位于日本海的北部和西北部有日本海盆，是最主要的海盆，另外东南部是大和海盆，还有西南部的对马海盆。日本海的东岸水深较浅，大陆棚较宽；海的西岸，特别是朝鲜半岛附近的水域，大陆架的延伸只有约30公里左右。黑潮（日本暖流）的一个分支即对马海流进入此海域。

The Sea of Japan (see below) is a marginal sea between the Japanese archipelago, Sakhalin, and the Asian mainland. The Japanese archipelago separates the sea from the Pacific Ocean. It is bordered by Japan, North Korea, Russia and South Korea. Like the Mediterranean Sea, it has almost no tides due to its nearly complete enclosure from the Pacific Ocean. This isolation also reflects in the fauna species and in the water salinity, which is lower than in the ocean. The sea has no large islands, bays or capes. Its water balance is mostly determined by the inflow and outflow through the straits connecting it to the neighboring seas and Pacific Ocean. Few rivers discharge into the sea and their total contribution to the water exchange is within 1%.