Heartwood of the Bodhi Tree: The Buddha’s Teaching on Voidness by Buddhadāsa Bhikkhu.

Three talks (“The Heart of Buddhism,” “All About Voidness,” and “Practicing With Voidness”) given to a Dhamma study group at Siriraj Hospital, Bangkok, on 17th December 1961 , 7th and 21st January 1962.

Translated from the Thai (แก่นพุทธศาสน์) by Dhammavicayo. Revised and edited by Santikaro Bhikkhu. Wisdom Publications, Boston, 1994. 150 p. ISBN: 0-86171-035-5