This book presents an account of alignment shifts in Iranian languages, and covers a time-span of some two and half millennia. It blends data from more than 20 Iranian languages, past and present, with theoretical discussion of alignment (ergativity, accusativity), subjecthood, diachronic syntax and morphology. No specialist knowledge of the Iranian languages is presupposed. The most detailed analyses of single languages are from Kurdish, based on extensive original field-work. Ergativity in Iranian is shown to be most prominently linked to the notion of Non-Canonical Subject. The results have repercussions for theories of alignment and grammatical relations, morphosyntactic change, and for comparative syntax of Indo-European.