This is the first type of work in the history of Sanskrit linguistics. Though a number of studies on the grammatical and linguistic aspects of Vedic and Classical Sanskrit have been carried out, yet a comprehensive study taking into account various aspects of Sanskrit language from the point of modern linguistics, has remained a desideratum. The few efforts made in this direction are neither comprehensive nor systematic in their treatment. Thus a need for an exhaustive and comprehensive study of the two stages of the development of Sanskrit language from the point of view of modern linguistics, was felt since long. Keeping in view of the necessity of such a study, this work dealing with the phonology of the two stages has been carried out. The contrastive study of phonology of Vedic and Classical Sanskrit will cater to the need of Sanskrit scholars and students interested into contrastive and comparative analysis of Vedic and Classical Sanskrit.