“Human life must be respected and protected absolutely from the moment of conception. From the first moment of his existence, a human being must be recognized as having the rights of a person—among which is the inviolable right of every innocent being to life.” (CCC, No. 2270)

“Formal cooperation in an abortion constitutes a grave offense. The Church attaches the canonical penalty of excommunication to this crime against human life. ‘A person who procures a completed abortion incurs excommunication latae sententiae… by the very commission of the offense, and subject to the conditions provided by Canon Law. The Church does not thereby intend to restrict the scope of mercy. Rather, she makes clear the gravity of the crime committed, the irreparable harm done to the innocent who is put to death, as well as to the parents and the whole of society.” (CCC, No. 2272)

ABORTION

Catechism of the Catholic Church
# 2270-2275

Living the Gospel of Life (1998)
United States Conference of Catholic Bishops

Evangelium Vitae (The Gospel of Life):On the Value and Inviolability of Human Life (1995)
Encyclical of Pope John Paul II

Donum Vitae: Instruction on Respect for Human Life (1987)
Instruction by Cardinal Joseph Ratzinger, Prefect for the Congregation for the Doctrine of the Faith

Declaration on Procured Abortion (1974)
Sacred Congregation for the Doctrine of the Faith

Other documents on the Dignity of Human Life
available on the United States Conference of Catholic Bishops (USCCB) site