 His book titled "Rediscovering Vatican II – Ecumenism and Interreligious Dialogue", was published 2005 and marked the 40th anniversary of the Vatican's ecumenism declaration "Nostra aetate".The book made a significant contribution to ongoing international inter-religious dialogue.In 1990, Cassidy was appointed a Companion of the Order of Australia (AC) in "recognition of [his] service to (the) religion and to international affairs".