The Sarvāstivāda is one of the most important Buddhist Schools during the period of Abhidharma development. An understanding of its doctrinal development is indispensable for gaining a proper perspective of the development in Buddhist thoughts in India as a whole. Its doctrine of sarvāstitva — the tri-temporal existence of dharma-s — had had tremendous impact on the doctrines of not only the so called Abhidharma schools, but also those of the Mahāyāna; either directly or indirectly, positively or negatively. Accordingly, even those aspiring to acquire insight into the sources of Mahāyāna thoughts ought to be sufficiently acquainted with the fundamental doctrines of the school. This publication is one of the first in English – if not actually the first – that deals comprehensively with all the major Sarvāstivāda doctrines within a single volume. The first edition was published in 2002 by the Centre of Buddhist Studies, Sri Lanka. The present third edition is a substantial revision of the second edition published in 2004. Besides a comprehensive index, a glossary of Sanskrit terminologies has also been added in this edition for the convenience of those unfamiliar with the Sanskrit language.