Proto-language may either refer to a language that preceded a certain set of given languages, or to system of communication during a stage in glottogony that may not yet be properly called a language.

A relative proto-language is a language that reflects an earlier state in a language family. The emphasis is that it is reconstructed by comparing different members of the language family for which records are available. Examples are Proto-Indo-European and Proto-Bantu; see also Proto-World Language.

An absolute proto-language, as defined by linguist Derek Bickerton, is a primitive form of communication lacking:

• a fully-developed syntax
• tense, aspect, auxiliary verbs, etc.
• a closed (i.e. non-lexical) vocabulary

The "me Tarzan, you Jane" nature of proto-language in this last sense is evident in pidgins, some features of early childhood language, and the language of adults who were deprived of language during the critical period (such as the feral child Genie). Derek Bickerton suggests language evolved from this kind of proto-language in a linguistic 'big bang'. But see also Terrence Deacon's arguments in his book The Symbolic Species for a radically different point of view.