《亚当斯-奥尼斯条约》又称《横贯大陆条约》或者是《佛罗里达州条约》，是1819年时的美国和西班牙签署的条约，其中西班牙决定把佛罗里达州卖给美国并和美国订出与新西班牙总督辖区的边界。条约解决了两国之间存在的边界争端，且被认为是美国外交的胜利。签署的原因在于西班牙当时和北美地区的领土边界问题不断增加，除了当时美国和英国刚结束美国独立战争外，拉丁美洲独立战争也紧接着爆发。由于西班牙方面没有能力派人定居或者驻军佛罗里达州，使得该地成为自身殖民统治的负担。

西班牙最终决定签署《亚当斯-奥尼斯条约》而割让领土给美国，以换取西班牙德克萨斯州沿着沙宾河有着稳定的边界。这个条约则以500万美元确立了美国领土的边界，并且该分界则通过落基山脉至部太平洋西岸地区；另外美国还放弃在西班牙德克萨斯州部分的领土，以及在沙宾河西边的西班牙殖民地的其他领地也归还给西班牙政府。

The Adams–Onís Treaty of 1819, also known as the Transcontinental Treaty, the Florida Purchase Treaty, or the Florida Treaty, was a treaty between the United States and Spain in 1819 that ceded Florida to the U.S. and defined the boundary between the U.S. and New Spain. It settled a standing border dispute between the two countries and was considered a triumph of American diplomacy. It came in the midst of increasing tensions related to Spain's territorial boundaries in North America vs. the United States and Great Britain in the aftermath of the American Revolution; and also during the Latin American Wars of Independence. Florida had become a burden to Spain, which could not afford to send settlers or garrisons. Madrid decided to cede the territory to the United States through the Adams–Onís Treaty in exchange for settling the boundary dispute along the Sabine River in Spanish Texas. The treaty established the boundary of U.S. territory and claims through the Rocky Mountains and west to the Pacific Ocean, in exchange for the U.S. paying residents' claims against the Spanish government up to a total of $5,000,000 and relinquishing the US claims on parts of Spanish Texas west of the Sabine River and other Spanish areas, under the terms of the Louisiana Purchase.