不列颠尼亚（英文：Britannia）是罗马帝国对不列颠岛的拉丁语称呼，后据此设立不列颠尼亚行省。这一拉丁语称谓，后又衍生出守护不列颠岛的女神名称。若以读音论，实以“不列塔尼亚”最接近原始发音，所以一些架空、奇幻小说中相当于英国的地方，往往译作不列塔尼亚。

罗马帝国不列颠尼亚行省的疆域，包括英格兰和威尔士的绝大部分地区，其北侧以哈德良长城作为和苏格兰之间的边境。哈德良长城以北地区，罗马人称做加勒多尼亚。

不列颠尼亚被罗马人神化，衍生不列颠女神。后成为现代英国的化身和象征，她的现代形象通常是身披盔甲，手持三叉戟和盾。

Britannia was the Greek and Roman term for the geographical region of Great Britain which was inhabited by the Britons and is the name given to the female personification of the island. It is a term still used to refer to the island today. The name is Latin, and derives from the Greek form Prettanike or Brettaniai, which originally designated a collection of islands with individual names, including Albion or Great Britain; however, by the 1st century BC, Britannia came to be used for Great Britain specifically. In AD 43 the Roman Empire began its conquest of the island, establishing a province they called Britannia, which came to encompass the parts of the island south of Caledonia (roughly Scotland). The native Celtic inhabitants of the province are known as the Britons. In the 2nd century, Roman Britannia came to be personified as a goddess, armed with a trident and shield and wearing a Corinthian helmet.