This chapter surveys pathways that have been proposed for how ergative alignment develops diachronically in an accusative language. The most common source cited for ergative alignment is a clausal nominalization. This is because the v (or n) in the nominalization has the same case-licensing featural composition as transitive v in an ergative language: 1) the external argument in the specifier is assigned inherent (typically genitive) case; and 2) there is no structural licensing capability for an object. After reanalysis, the external argument continues to receive inherent case, and the object values nominative case with T, resulting in an ergative pattern in transitive clauses. Other proposed sources are also typically intransitive constructions lacking accusative objects and in which the external argument is assigned inherent case or is packaged as a PP, for example possessive constructions and passives