The Eastern Algonquian languages constitute a subgroup of the Algonquian languages. Prior to European contact, Eastern Algonquian consisted of at least 17 languages, whose speakers collectively occupied the Atlantic coast of North America and adjacent inland areas, from what are now the Maritimes of Canada to North Carolina. The available information about individual languages varies widely. Some are known only from one or two documents containing words and phrases collected by missionaries, explorers or settlers, and some documents contain fragmentary evidence about more than one language or dialect. Many of the Eastern Algonquian languages were greatly affected by colonization and dispossession. Miꞌkmaq and Malecite-Passamaquoddy have appreciable numbers of speakers, but Western Abenaki and Lenape (Delaware) are each reported to have fewer than 10 speakers after 2000.

Eastern Algonquian constitutes a separate genetic subgroup within Algonquian. Two other recognized groups of Algonquian languages, Plains Algonquian and Central Algonquian, are geographic but do not refer to genetic subgroupings.

A consensus classification of the known Eastern Algonquian languages and dialects by Goddard (1996) is given below with some emendation, for example treatment of Massachusett and Narragansett as distinct languages. In the case of poorly attested languages, particularly in southern New England, conclusive classification of written records as representing separate languages or dialects may be ultimately impossible.

The Max Planck Institute for Evolutionary Anthropology classifies the Eastern Algonquian languages within their Glottolog database as follows:

The languages assigned to the Eastern Algonquian group are hypothesized to descend from an intermediate common ancestor proto-language, referred to as Proto-Eastern Algonquian (PEA). By virtue of their common ancestry, the Eastern Algonquian languages constitute a genetic subgroup, and the individual Eastern Algonquian languages descend from PEA. By contrast, other Algonquian languages are hypothesized to descend directly from Proto-Algonquian, the ultimate common language ancestor of the Algonquian languages.

In historical linguistics in general, the primary criterion for status as a genetic subgroup is that there are shared innovations assigned to the proposed subgroup that cannot be assigned to the ultimate ancestor language. A complex series of phonological and morphological innovations define Eastern Algonquian as a subgroup. "There is less diversity, by any measure, among [Eastern Algonquian languages] as a group than among the Algonquian languages as a whole or among the non-Eastern languages."

The validity of PEA as a genetic subgroup has been disputed by Pentland and Proulx. Pentland questions the Eastern Algonquian status of the southern New England languages and Powhatan and Carolina Algonquian. Proulx has proposed that the similarities can be explained as the result of diffusion. Goddard has countered that the extent of the similarities would require extensive diffusion very early in the breakup of the Eastern Algonquian languages and that such a position would be difficult in principle to differentiate from analyzing PEA as a genetic subgroup.

Similarities among subsets of some of the Eastern Algonquian languages have led to several proposals for further subgroupings within Eastern Algonquian: Abenakian, Southern New England Algonquian (SNEA), and Delawaran, with the latter consisting of Mahican and Common Delaware, a further subgroup. The amount of evidence for each subgrouping varies, and the incomplete record for many parts of the Eastern Algonquian area makes interpretation of relations between the languages difficult.