Proto-Algonquian (commonly abbreviated PA) is the proto-language from which the various Algonquian languages are descended. It is generally estimated to have been spoken around 2,500 to 3,000 years ago, but on the question of where it was spoken, there is less agreement. The Algonquian family, which is a branch of the larger Algic language family, is usually divided into three subgroups: Eastern Algonquian, which is a genetic subgroup, and Central Algonquian and Plains Algonquian, both of which are areal groupings. In the historical linguistics of North America, Proto-Algonquian is one of the best studied, most thoroughly reconstructed proto-languages. It is descended from Proto-Algic.
Most Algonquian languages are similar enough that their relatedness has been recognized for centuries and was commented on by the early English and French colonists and explorers. For example, in 1787 (over a decade before Sir William Jones' famous speech on Indo-European), the theologian and linguist Jonathan Edwards Jr. deduced that the Algonquian languages of the eastern and central United States were "radically the same" ('radically' meaning having a common 'root', since radix is Latin for 'root'), and contrasted them with the neighboring Iroquoian languages. The earliest work on reconstructing the Algonquian proto-language was undertaken by the linguists Truman Michelson and Leonard Bloomfield. In 1925 Bloomfield reconstructed what he called "Primitive Central Algonquian", using what were at the time the four best-attested Algonquian languages: Fox, Ojibwe, Menominee, and Plains Cree. Following his initial reconstructions, investigations of other languages revealed that his "Primitive Central Algonquian" was essentially equivalent to Proto-Algonquian. Bloomfield wrote a refinement and expansion of his reconstruction in 1946, and his two papers remain the starting point for all research and reconstructions of Proto-Algonquian. In the years since there has been an enormous amount of comparative work undertaken on the Algonquian family.