长岛（英语：Long Island），是位于北美洲大西洋岸的岛屿，行政上属于美国纽约州的一部份。长岛长190公里，宽约20到30公里，从纽约港伸入北大西洋；向北它隔长岛海湾与康涅狄格州和罗德岛相望；向南是北大西洋在北美洲边上的大海湾；长岛东端分为南北两个叉，分别称为南叉和北叉。

长岛的西部是纽约市的市区布鲁克林和皇后区，其东是纽约州的纳苏郡和苏福克郡。纽约人说「长岛」的话通常只指这两个郡，很少人会将皇后区或布鲁克林也算作长岛一部分。

长岛的北叉上出产长岛葡萄酒。

从地质学的角度看，长岛是两条冰川堆积物，主要成分是在海岸上堆积起来的巨石和石子，上面又铺了一层沙质的浮土。造成这个堆积的是威士顿康星冰川最近的两次延伸。从地理学角度来说，长岛实际上是半岛，与美洲大陆隔哈德逊河河口的潮汐带。长岛东部依然是一个农业地区，包括许多葡萄园和传统的机械化农庄。渔业在那里也依然存在。

Long Island is an island located just off the northeast coast of the United States and a region within the U.S. state of New York. Stretching east-northeast from New York Harbor into the Atlantic Ocean, the island comprises four counties: Kings and Queens (these form the New York City boroughs of Brooklyn and Queens, respectively) to the west; then Nassau and Suffolk to the east. However, many people in the New York metropolitan area (even those living in Queens and Brooklyn) colloquially use the term "Long Island" (or "The Island") exclusively to refer to the Nassau-Suffolk county area collectively, which is mainly suburban in character. North of the island is Long Island Sound, across from which lie the states of Connecticut and a small part of Rhode Island.