Catholic teachings on sexual morality draw from natural law, Sacred Scripture and Sacred Tradition and are promulgated authoritatively by the Magisterium. Sexual morality evaluates the goodness of sexual behavior, and often provides general principles by which one is able to evaluate the morality of specific actions.
The Catholic Church teaches that human life and human sexuality are both inseparable and sacred.  Because Catholics believe God created human beings in his own image and likeness and that he found everything he created to be "very good," the Catholic Church teaches that human body and sex must likewise be good. The Catechism teaches that "the flesh is the hinge of salvation." The Church considers the expression of love between husband and wife to be an elevated form of human activity, joining as it does, husband and wife in complete mutual self-giving, and opening their relationship to new life. “The sexual activity, in which husband and wife are intimately and chastely united with one another, through which human life is transmitted, is, as the recent Council recalled, ‘noble and worthy.’” It is in cases in which sexual expression is sought outside sacramental marriage, or in which the procreative function of sexual expression within marriage is deliberately frustrated, that the Catholic Church expresses grave moral concern.
However the Church does teach that sexual intercourse outside of marriage is contrary to its purpose. The "conjugal act" aims at a deeply personal unity, a unity that, beyond union in one flesh, leads to forming one heart and soul" since the marriage bond is to be a sign of the love between God and humanity.
Among the sins gravely contrary to chastity are masturbation, fornication, pornography, homosexual practices and artificial contraception. Besides being considered a grave sin, the procurement or assistance in abortion can carry the penalty of excommunication.
Sources of Catholic sexual morality
Natural law (Latin: lex naturalis) is an ethical theory that posits the existence of a law whose content is set by nature and that therefore has validity everywhere. Despite pagan associations with natural law theory, a number (though not all) of the early Church Fathers sought to incorporate it into Christianity (the suspect devotion of the Stoics to pagan worship no doubt aided in this adoption).
the rational creature is subject to Divine providence in the most excellent way, in so far as it partakes of a share of providence, by being provident both for itself and for others. Wherefore it has a share of the Eternal Reason, whereby it has a natural inclination to its proper act and end: and this participation of the eternal law in the rational creature is called the natural law.
Natural law is a basic source for Catholic teachings on sexual morality.
The creation stories in Genesis 1-3 provide insights into anthropology that inform Catholic sexual morality. The following verses are frequently cited in Catholic studies of sexual morality:
- "God created man in his own image, in the image of God he created him; male and female he created them. And God blessed them, and God said to them, 'Be fruitful and multiply, and fill the earth and subdue it'" (Gen 1:27)
- "the Lord God caused a deep sleep to fall upon the man, and while he slept took one of his ribs and closed up its place with flesh; and the rib which the Lord God had taken from the man he made into a woman and brought her to the man. Then the man said, "This at last is bone of my bones and flesh of my flesh; she shall be called Woman, because she was taken out of Man." Therefore a man leaves his father and his mother and cleaves to his wife, and they become one flesh. And the man and his wife were both naked, and were not ashamed." (Gen 2:21-25)
- "To the woman he said, 'I will greatly multiply your pain in childbearing; in pain you shall bring forth children, yet your desire shall be for your husband, and he shall rule over you.'" (Gen 3:16)
Two of the Ten Commandments directly address sexual morality, forbidding adultery and coveting a neighbor's wife. See Exodus 20:14, 17; Deuteronomy 5:18, 21.
Jesus comments on these commandments in Matthew 5:27-28: "You have heard that it was said, `You shall not commit adultery.' But I say to you that every one who looks at a woman lustfully has already committed adultery with her in his heart."
Jesus makes reference to the passages from Genesis in his teachings on marriage in Matthew 19: "Have you not read that he who made them from the beginning made them male and female, and said, `For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh'? So they are no longer two but one flesh. What therefore God has joined together, let not man put asunder."
Fathers of the church
Augustine of Hippo, having lived a hedonistic lifestyle in his early youth, among hooligans whom he treated as friends with benefits, later followed the strictly dualistic religion of Manicheanism, which was deeply hostile to the material world, despising sexual activity. Eventually, under the influence of his Christian mother, Augustine converted to Christianity, and later wrote movingly of this conversion in his Confessions, including details of the sexually-related aspects. The following passage from his autobiography describes a critical turning point in his change of sexual morality:
So quickly I returned to the place where Alypius was sitting; for there had I put down the volume of the apostles, when I rose thence. I grasped, opened, and in silence read that paragraph on which my eyes first fell: "Not in rioting and drunkenness, not in chambering and wantonness, not in strife and envying; but put ye on the Lord Jesus Christ, and make not provision for the flesh, to fulfil the lusts thereof." [Romans 13:13-14] No further would I read, nor did I need... 
Saint Thomas Aquinas dealt with sexual morality as an aspect of the virtue of temperance, and incorporates Scripture throughout his account. In his Summa Theologiae he writes about chastity:
The word "chastity" is employed in two ways. First, properly; and thus it is a special virtue having a special matter, namely the concupiscences relating to venereal pleasures. Secondly, the word "chastity" is employed metaphorically: for just as a mingling of bodies conduces to venereal pleasure which is the proper matter of chastity and of lust its contrary vice, so too the spiritual union of the mind with certain things conduces to a pleasure which is the matter of a spiritual chastity metaphorically speaking, as well as of a spiritual fornication likewise metaphorically so called. For if the human mind delight in the spiritual union with that to which it behooves it to be united, namely God, and refrains from delighting in union with other things against the requirements of the order established by God, this may be called a spiritual chastity, according to 2 Cor. 11:2, "I have espoused you to one husband, that I may present you as a chaste virgin to Christ." If, on the other hand, the mind be united to any other things whatsoever, against the prescription of the Divine order, it will be called spiritual fornication, according to Jer. 3:1, "But thou hast prostituted thyself to many lovers." Taking chastity in this sense, it is a general virtue, because every virtue withdraws the human mind from delighting in a union with unlawful things. Nevertheless, the essence of this chastity consists principally in charity and the other theological virtues, whereby the human mind is united to God.
Recent magisterial teachings
- Casti connubii (1930) by Pope Pius XI
- Casti connubii was written in part as a response to the decision of the Anglican Lambeth Conference in 1930 that taught the legitimacy of the use of contraception in some circumstances.
- "any use whatsoever of matrimony exercised in such a way that the act is deliberately frustrated in its natural power to generate life is an offense against the law of God and of nature, and those who indulge in such are branded with the guilt of a grave sin."
- Humanae vitae (1968) by Pope Paul VI
- Theology of the Body by Pope John Paul II
- Evangelium vitae (1995) by Pope John Paul II
- Donum vitae (1987) by the Congregation for the Doctrine of the Faith
- Veritatis splendor (1993) by Pope John Paul II
- Catechism of the Catholic Church (1992)
- Deus Caritas Est (2006)
The Catholic teaching on specific subjects
Catholicism defines chastity as the virtue that moderates the sexual appetite. Unmarried Catholics express chastity through sexual abstinence. Sexual intercourse within marriage is considered chaste when it retains the twofold significance of union and procreation. Pope John Paul II wrote,
At the center of the spirituality of marriage, therefore, there lies chastity not only as a moral virtue (formed by love), but likewise as a virtue connected with the gifts of the Holy Spirit—above all, the gift of respect for what comes from God (donum pietatis). This gift is in the mind of the author of the Ephesians when he exhorts married couples to "defer to one another out of reverence for Christ" (Eph 5:21). So the interior order of married life, which enables the manifestations of affection to develop according to their right proportion and meaning, is a fruit not only of the virtue which the couple practice, but also of the gifts of the Holy Spirit with which they cooperate. 
Because sex is considered chaste only within context of marriage it has come to be called the nuptial act in Catholic passages. Among Catholics, the nuptial act is considered to be the conjoining of two human beings through sexual intercourse, considered an act of love between two married persons, and is considered in this way, a gift from God. While discussing chastity, the Catechism of the Catholic Church lists several transgressions and sins against it.
Contraception is defined as "every action which, whether in anticipation of the conjugal act, or in its accomplishment, or in the development of its natural consequences, proposes, whether as an end or as a means, to render procreation impossible." Contraception so defined is intrinsically evil.
As Pope John Paul II taught in Familiaris Consortio,
Thus the innate language that expresses the total reciprocal self-giving of husband and wife is overlaid, through contraception, by an objectively contradictory language, namely, that of not giving oneself totally to the other. This leads not only to a positive refusal to be open to life but also to a falsification of the inner truth of conjugal love, which is called upon to give itself in personal totality.... the difference, both anthropological and moral, between contraception and recourse to the rhythm of the cycle . . . involves in the final analysis two irreconcilable concepts of the human person and of human sexuality.
- Health uses of contraceptives
Occasionally, a substance that is most commonly used as a contraceptive may be used to treat a medical condition. One example is the use of hormonal contraception to treat endometriosis. Because such treatments are used without contraceptive intent, they are not morally considered contraception.
The use of condoms to prevent disease is a more controversial issue, with theologians arguing both sides. Unlike drugs and surgical procedures, however, the current consensus is that any use of a condom is morally contraceptive and thus a sin.
Issues surrounding the Roman Catholic Church and AIDS have become highly controversial in the past twenty years, primarily because many prominent religious leaders have publicly declared their opposition to the use of condoms as a disease preventative. Other issues involve religious participation in global health care services and collaboration with secular organizations such as UNAIDS and the World Health Organization.
Fornication is carnal union between an unmarried man and an unmarried woman. It is gravely contrary to the dignity of persons and of human sexuality which is naturally ordered to the good of spouses and the generation and education of children. Moreover, it is a grave scandal when there is corruption of the young. 
Homosexuality refers to relations between men or between women who experience an exclusive or predominant sexual attraction toward persons of the same sex. It has taken a great variety of forms through the centuries and in different cultures. Its psychological genesis remains largely unexplained. Basing itself on Sacred Scripture, which presents homosexual acts as acts of grave depravity,141 tradition has always declared that "homosexual acts are intrinsically disordered."142 They are contrary to the natural law. They close the sexual act to the gift of life. They do not proceed from a genuine affective and sexual complementarity. Under no circumstances can they be approved.
Pornography consists in removing real or simulated sexual acts from the intimacy of the partners, in order to display them deliberately to third parties. It offends against chastity because it perverts the conjugal act, the intimate giving of spouses to each other. It does grave injury to the dignity of its participants (actors, vendors, the public), since each one becomes an object of base pleasure and illicit profit for others. It immerses all who are involved in the illusion of a fantasy world. It is a grave offense. Civil authorities should prevent the production and distribution of pornographic materials.
Prostitution does injury to the dignity of the person who engages in it, reducing the person to an instrument of sexual pleasure. The one who pays sins gravely against himself: he violates the chastity to which his Baptism pledged him and defiles his body, the temple of the Holy Spirit. Prostitution is a social scourge. It usually involves women, but also men, children, and adolescents (The latter two cases involve the added sin of scandal.). While it is always gravely sinful to engage in prostitution, the imputability of the offense can be attenuated by destitution, blackmail, or social pressure.
Rape is the forcible violation of the sexual intimacy of another person. It does injury to justice and charity. Rape deeply wounds the respect, freedom, and physical and moral integrity to which every person has a right. It causes grave damage that can mark the victim for life. It is always an intrinsically evil act. Graver still is the rape of children committed by parents (incest) or those responsible for the education of the children entrusted to them.
- Catholic theology of the body
- Catholics for Choice
- Christian views on contraception
- Homosexuality and Catholicism
- Sexual ethics
- Moral theology
Catholic Church (1997). Catechism of the Catholic Church: with modifications from the editio typica (Second Edition ed.). Garden City, N.Y: Doubleday. ISBN 0-385-50819-0. http://www.usccb.org/catechism/text. Retrieved 2009-03-21.
- ↑ Catechism of the Catholic Church, 2331–2400
- ↑ Catechism of the Catholic Church, 1015
- ↑ "Humanae Vitae, no. 11"
- ↑ Catechism of the Catholic Church, 1643
- ↑ Catechism of the Catholic Church, 1617
- ↑ Catechism of the Catholic Church, 2351–2357
- ↑ Catechism of the Catholic Church, 2370
- ↑ Catechism of the Catholic Church, 2272
- ↑ "Natural Law," International Encyclopedia of the Social Sciences.
- ↑ ST I-II Q91 a2 corp
- ↑ St. Augustine, Confessions, Book 8, Chapter 12
- ↑ St. Thomas Aquinas, Summa Theologiae, II-II, Question 151, Article 2, corp.
- ↑ Catechism of the Catholic Church, 
- ↑ Thomas Aquinas, Summa Theologia I-II q. 60 a. 5; Catholic Encyclopedia, "Chastity"
- ↑ Humanae vitae 12
- ↑ Pope John Paul II, General Audience, Wednesday, November 14, 1984.
- ↑ Catechism of the Catholic Church 2337-2350, 2337–2350
- ↑ Humanae vitae 14, 
- ↑ Familiaris Consortio 32, 
- ↑ Hardon, John (2000). "Endometriosis". Modern Catholic Dictionary. Eternal Life. ISBN 096729892X. http://www.catholicculture.org/culture/library/dictionary/index.cfm?id=33323.
- ↑ James T. Bretzke, S.J. (26 March,). "The Lesser Evil". America Magazine. http://americamagazine.org/content/article.cfm?article_id=5371. Retrieved 2008-05-16.
- ↑ Guevin, Benedict; Martin Rhonheimer (Spring 2005). "Debate: On the Use of Condoms to Prevent Acquired Immune Deficiency Syndrome". The National Catholic Bioethics Quarterly: 35—48.
- ↑ May, William E. (Summer/Fall 2007). "The Theological Significance of Consummation of Marriage, Contraception, Using Condoms to Prevent HIV, and Same-Sex Unions". Josephinum Journal of Theology (Pittsfield, Massachusetts: Catholic Library Association) 14 (2): 207—217.
- ↑ Catechism of the Catholic Church 2353, 2353
- ↑ Catechism of the Catholic Church 2357, 2357
- ↑ Catechism of the Catholic Church 2351, 2351
- ↑ Catechism of the Catholic Church 2352, 2352
- ↑ Catechism of the Catholic Church 2354, 2354
- ↑ Catechism of the Catholic Church 2355, 2355
- ↑ Catechism of the Catholic Church 2356, 2356