亚得里亚海（意大利语：Mar Adriatico，斯洛文尼亚语：Jadransko morje，克罗地亚语：Jadransko more，阿尔巴尼亚语：Deti Adriatik），是地中海的一部份水域，分隔了亚平宁半岛和巴尔干半岛，也分隔了亚平宁山脉与狄那里克阿尔卑斯山脉及其临近地区。亚得里亚海西岸属于意大利，东岸则分别属于斯洛文尼亚、克罗地亚、波斯尼亚和黑塞哥维那、蒙特内哥罗和阿尔巴尼亚。亚得里亚海透过位于其南部的奥特朗托海峡与爱奥尼亚海相连。波河、阿迪杰河、奥凡托河等河流流入亚得里亚海；海中有近1200个岛屿，其中只有69个有人居住。

The Adriatic Sea /ˌeɪdriˈætᵻk/ is a body of water separating the Italian Peninsula from the Balkan peninsula and the Apennine Mountains from the Dinaric Alps and adjacent ranges. The Adriatic is the northernmost arm of the Mediterranean Sea, extending from the Strait of Otranto (where it connects to the Ionian Sea) to the northwest and the Po Valley. The countries with coasts on the Adriatic are Italy, Croatia, Albania, Montenegro, Bosnia-Herzegovina, and Slovenia. The Adriatic contains over 1,300 islands, mostly located along its eastern, Croatian, coast. It is divided into three basins, the northern being the shallowest and the southern being the deepest, with a maximum depth of 1,233 metres (4,045 ft). The Otranto Sill, an underwater ridge, is located at the border between the Adriatic and Ionian Seas. The prevailing currents flow counterclockwise from the Strait of Otranto, along the eastern coast and back to the strait along the western (Italian) coast. Tidal movements in the Adriatic are slight, although larger amplitudes are known to occur occasionally. The Adriatic's salinity is lower than the Mediterranean's because the Adriatic collects a third of the fresh water flowing into the Mediterranean, acting as a dilution basin. The surface water temperatures generally range from 30 °C (86 °F) in summer to 12 °C (54 °F) in winter, significantly moderating the Adriatic Basin's climate.