Catechism of the Catholic Church on Euthanasia
Article 5 of the Catechism, on the Fifth Commandment, sections 2276 to 2279, has information on the sanctity of human life and the issue of euthanasia.
Declaration on Euthanasia
Sacred Congregation for the Doctrine of the Faith 1980 Declaration on Euthanasia.
USCCB Secretariat of Pro-Life Activities - Euthanasia Articles
This site contains more Church documents, articles, columns, fact sheets, and other information on the issue of euthanasia and physician assisted suicide.