Linguistic reconstruction is the practice of establishing the features of an unattested ancestor language of one or more given languages. There are two kinds of reconstruction:
- Internal reconstruction uses irregularities in a single language to make inferences about an earlier stage of that language – that is, it is based on evidence from that language alone.
- Comparative reconstruction, usually referred to just as reconstruction, establishes features of the ancestor of two or more related languages, belonging to the same language family, by means of the comparative method. A language reconstructed in this way is often referred to as a proto-language (the common ancestor of all the languages in a given family); examples include Proto-Indo-European, Proto-Dravidian, etc.
Texts discussing linguistic reconstruction commonly preface reconstructed forms with an asterisk (*) to distinguish them from attested forms.
An attested word from which a root in the proto-language is reconstructed is a reflex. More generally, a reflex is the known derivative of an earlier form, which may be either attested or reconstructed. Reflexes of the same source are cognates.
First, languages that are thought to have arisen from a common proto-language must meet certain criteria in order to be grouped together; this is a process called subgrouping. Since this grouping is based purely on linguistics, manuscripts and other historical documentation should be analyzed to accomplish this step. However, the assumption that the delineations of linguistics always align with those of culture and ethnicity must not be made. One of the criteria that the grouped languages usually exemplify shared innovation. This means that the languages must show common changes made throughout history. In addition, most grouped languages have shared retention. This is similar to the first criterion, but instead of changes, they are features that have stayed the same in both languages.
Because linguistics, as in other scientific areas, seeks to reflect simplicity, an important principle in the linguistic reconstruction process is to generate the least possible number of phonemes that correspond to available data. This principle is again reflected when choosing the sound quality of phonemes, as the one which results in the fewest number of changes (with respect to the data) is preferred. 
- Anthony Fox, Linguistic Reconstruction: An Introduction to Theory and Method (Oxford University Press, 1995) ISBN 0-19-870001-6.
- Henry M. Hoenigswald, Language Change and Linguistic Reconstruction (University of Chicago Press, 1960) ISBN 0-226-34741-9.
- Fox, Anthony (1995). Linguistic Reconstruction: An Introduction to Theory and Method. Oxford University Press. ISBN 9780198700012.
- Historical linguistics 1995 : selected papers from the 12th International Conference on Historical Linguistics, Manchester, August 1995. Smith, John Charles, 1950-, Bentley, Delia., Hogg, Richard M., Bergen, Linda van. Amsterdam: John Benjamins. 1998–2000. ISBN 9027236666. OCLC 746925995.