Summary This article is an updated version of the first and second editions of the original manuscript by Professor Michael K. Duffey. It covers the religious and philosophical grounds for conscientious objection to military service. The grounds for refusal in Judaism, Christianity, Islam, Hinduism, and Buddhism are addressed. Since the number of countries adopting conscription is diminishing today, the problem of conscientious objection to military service should be eliminated. Both the United Nations and the European Court of Human Rights have come to recognize that the right to conscientious objection to military service is guaranteed under the freedom of conscience and religion. A contested issue is whether people may exercise the right of conscientious objection to specific armed conflict.