The Japan/East Sea (JES) is a large, multi-ported, semi-enclosed sea situated between the subtropical and subpolar zones. It exhibits most oceanic phenomena (e.g., wind-driven and buoyancy-driven boundary currents, a subpolar jet and front, and mesoscale eddies) and processes (e.g., intense air-sea interaction, subduction and deep convection, and topographic trapping). JES circulation is driven by wind and thermohaline forcing, tides, and throughflow; however, this circulation is controlled largely by its bottom topography, especially by the large Yamato Rise in the center of the southern half, the large Japan Basin to the north, Ulleung Basin to the west, Yamato Basin to the east, and numerous seamounts. Inflow is primarily through the Korea/Tsushima Strait in the south and the outflow is primarily through the Tsugaru and Soya Straits in the east; however, there is weak inflow seasonally through the shallow Tatar/Mamiya Strait in the north. For these reasons, and due to its small size compared to an ocean basin, the JES is a convenient natural laboratory for numerical modeling and observation of ocean circulation phenomena and processes.