芬兰湾（芬兰语：Suomenlahti；爱沙尼亚语：Soome laht；俄语：Финский залив, Finskiy zaliv；瑞典语：Finska viken）是波罗的海东部的大海湾，位于芬兰、爱沙尼亚之间，伸展至俄罗斯圣彼德堡为止。芬兰湾形状细长，长度约为400公里，平均水深为40米，最深处115米。海水含盐量低，深度和含盐量均自东向西逐渐增加，并有3-5月的封冻期。主要注入的河流有从圣彼德堡出海的涅瓦河。湾内主要城市有芬兰的赫尔辛基、爱沙尼亚的塔林及俄罗斯的圣彼德堡。

芬兰湾形状细长，面积约3万平方公里。东西长约400公里，平均水深为40米，入口处宽70公里，中部最宽处130公里。南北19～128公里。北岸陡峭、曲折，多岛屿；东、南岸低平。

The Gulf of Finland (Finnish:Suomenlahti; Estonian:Soome laht; Russian:Фи́нский зали́в, tr.Finskiy zaliv;IPA: [ˈfʲinskʲɪj zɐˈlʲif]; Swedish:Finska viken) is the easternmost arm of the Baltic Sea. It extends between Finland (to the north) and Estonia (to the south) all the way to Saint Petersburg in Russia, where the river Neva drains into it. Other major cities around the gulf include Helsinki and Tallinn. The eastern parts of the Gulf of Finland belong to Russia, and some of Russia's most important oil harbours are located farthest in, near Saint Petersburg (including Primorsk). As the seaway to Saint Petersburg, the Gulf of Finland has been and continues to be of considerable strategic importance to Russia. Some of the environmental problems affecting the Baltic Sea are at their most pronounced in the shallow gulf.