This monograph aims to close the gap in our knowledge of the nature and pace of grammatical change during the formative period of today’s Indo-Aryan languages. During the 6th-12th c. the gradual erosion of the synthetic morphology of Old Indo-Aryan resulted ultimately in the remodelling of its syntax in the direction of the New Indo-Aryan analytic type. This study concentrates on the emergence and development of the ergative construction in terms of the passive-to-ergative reanalysis and the co-existence of the ergative construction with the old and new analytic passive constructions. Special attention is paid to the actuation problem seen as the tug of war between conservative and eliminative forces during their development. Other chapters deal with the evolution of grammatical and lexical aspect, causativization, modality, absolute constructions and subordination. This study is based on a wealth of new data gleaned from original poetic works in Apabhraṃśa (by Svayaṃbhādeva, Puṣpadanta, Haribhadra, Somaprabha et al.). It contains sections dealing with descriptive techniques of Medieval Indian grammarians (esp. Hemacandra). All the Sanskrit, Prakrit and Apabhraṃśa examples are consistently parsed and translated. The opus is cast in the theoretical framework of Functional Grammar of the Prague and Amsterdam Schools. It should be of particular interest to scholars and students of Indo-Aryan and general historical linguistics, especially those interested in the issues of morphosyntactic change and typology in their sociohistorical setting.