This paper aims to show the sources of the Lithuanian conjunction nei(gi) ‘than’ and its later development. The most archaic function of nei that can be found in Old Lithuanian texts is nei ‘and not’ as a type of sentence negation in a clause following another clause that does not contain a negation, with both clauses combined asyndetically. Examples can be divided into two subtypes, defined as unordered addition and temporal succession clauses in Dixon’s terms (Dixon 2009). The counterparts of nei are Latin ne-que and German und nicht. The next stage in the development of coordinate sentences with nei was correlative sentences of the type ne- ... nei(gi) ‘not ... nor’, which were very common in the 16th century. The correlative construction ne- ... nei(gi) ‘not ... nor’ traces back to juxtaposed clauses with narrow-scope negation, viz. p & q (‘We didn’t meet Marvin, and we didn’t meet Joan either’)—Haspelmath (2007, 16). Negative coordination of the type ne- ... nei(gi) underlies reduplicated connectives nei ... nei ‘neither ... nor’, which are widespread in modern Lithuanian. ne- ... nei(gi) also gave rise to the conjunction of comparative clauses nei(gi) ‘than’. (Pirm) nei(g) ‘before’, as a conjunction of temporal clauses, belongs to the latest chronological layer.