Incest laws by country fall across a wide spectrum. At one end, France, Spain, Portugal, Belgium, Brazil, and Argentina impose no criminal penalty on sexual relationships between consenting adult relatives. At the other, common law countries like the United States, United Kingdom, Canada, and Australia treat the same conduct as a serious crime, with maximum sentences reaching 14 years in Canada. Germany sits in the middle with shorter sentences, and Sharia-influenced systems define forbidden kinship more broadly than secular codes do. Even the countries that agree incest should be illegal disagree about which relationships count, whether consent matters, and whether first cousins can marry.
Where Consenting Adult Incest Is Not a Crime
France removed incest from its penal code in 1791 during the Revolution, and that approach held for more than two centuries. The underlying idea was that criminal law should not reach private conduct between adults absent a victim. As of late 2025, French legislators were considering a bill to reintroduce incest as a specific offense for the first time since the Revolutionary era, though the proposals focused on strengthening protections for minors rather than broadly criminalizing adult relationships.
Spain, Portugal, Belgium, Brazil, and Argentina follow the same model. Brazil’s penal code contains no provision that specifically bans sexual relations between adult relatives. Prosecution happens only when another crime is involved, such as sexual abuse of a minor or coercion.
This tolerance does not extend to marriage. French civil law explicitly prohibits marriage between direct ancestors and descendants, and between in-laws in the same lineage. Most countries in this group maintain comparable marriage bans in their civil codes: private sexual conduct goes unprosecuted, but the state will not formalize the relationship. Age of consent laws apply with full force regardless of family relationship, and several countries impose enhanced penalties when a family member abuses a minor.
Common Law Countries That Criminalize Incest
United States
Every U.S. state criminalizes incest to some degree, but definitions and penalties vary. New York classifies incest in the third degree as a Class E felony, covering sexual contact between people related as ancestors, descendants, siblings, or uncles and aunts with nephews and nieces. The statute applies regardless of whether the relationship is through whole or half blood, and extends to relatives connected through marriage.1New York State Senate. New York Penal Law 255.25 – Incest in the Third Degree A Class E felony in New York carries a maximum of four years in prison, with a minimum of one year for an indeterminate sentence.2New York State Senate. New York Penal Law 70.00 – Sentence of Imprisonment for Felony Across all states, maximum sentences for a first conviction typically run from three to twenty years depending on the jurisdiction, the degree of the family relationship, and whether a minor is involved. There is no broad federal incest statute; outside federal enclaves, military bases, and tribal lands, this is a state matter.
United Kingdom
Sections 64 and 65 of the Sexual Offences Act 2003 make it a crime to engage in penetrative sexual activity with an adult relative. The law covers a wide range of blood relationships: parents, grandparents, children, grandchildren, brothers, sisters, half-siblings, uncles, aunts, nephews, and nieces. Adoptive parents and adopted children are included. A conviction on indictment carries up to two years in prison.3Legislation.gov.uk. Sexual Offences Act 2003, Section 64 – Sex With an Adult Relative: Penetration Step-relatives and in-laws are not covered by sections 64 and 65, though separate provisions on family-member offenses against children (sections 25 through 27) do include step-parents and foster parents.4Crown Prosecution Service. Rape and Sexual Offences – Chapter 7: Key Legislation and Offences
Canada
Section 155 of the Canadian Criminal Code treats incest as an indictable offense with a maximum sentence of 14 years. It applies to anyone who has sexual intercourse with a person they know to be a parent, child, brother, sister, grandparent, or grandchild by blood, including half-siblings. When the other person is under 16, the minimum sentence rises to five years. The law allows a defense for individuals who acted under restraint, duress, or fear of the other person.
Australia
Each Australian state and territory sets its own incest law. In South Australia, sexual intercourse with a close family member (parent, child, sibling, half-sibling, grandparent, or grandchild) carries a maximum penalty of 10 years. Consent is not a defense. The law does not reach relatives connected only by marriage or adoption. Other Australian jurisdictions take broadly similar approaches with varying maximum sentences.
Germany’s Middle Path
Germany criminalizes incest but imposes lighter penalties than the common law countries. Section 173 of the German Criminal Code makes sexual intercourse between blood relatives an offense. Intercourse with a blood descendant carries up to three years in prison or a fine. Intercourse with a blood relative in the ascending line, or between natural siblings, carries up to two years or a fine.5Gesetze im Internet. German Criminal Code (Strafgesetzbuch) Section 173 – Sexual Intercourse Between Relatives Descendants and siblings who were under 18 at the time of the act face no criminal penalty, even though the older relative does. The exception reflects the view that the younger party in a family relationship is likely subject to unequal power dynamics.
Sharia-Influenced Legal Systems
Countries that build Islamic law into their legal frameworks define forbidden relationships through the concept of Mahram, which identifies relatives who may never marry each other. These prohibitions overlap with Western incest laws on parents, children, siblings, and grandparents, but they also reach categories that secular systems do not.
The most distinctive is milk kinship, known as Rada. A child breastfed by a woman other than the biological mother acquires a legal family bond with that woman and her relatives. The nursed child and the wet nurse’s biological children are treated as siblings and permanently forbidden from marrying. The principle is rooted in Islamic jurisprudence and pre-Islamic cultural tradition, and it is codified in the personal status laws of countries including Saudi Arabia, Iran, and Malaysia. Penalties for violating these prohibitions can be severe, including lengthy imprisonment or corporal punishment through religious courts, with the specifics depending on the country and the local interpretation of Islamic law.
First-Cousin Marriage: The Widest Split
No area of kinship law produces more disagreement across borders than the status of first cousins. In much of the world, cousin marriage is legal and in some cultures actively preferred. In others, it is void or criminalized. The split does not follow a clean geographic line.
The United Kingdom and Japan both permit cousin marriage without restriction. Japanese civil law bans marriage only between lineal blood relatives and collateral blood relatives within the third degree of kinship, which covers siblings, aunts and uncles, and nephews and nieces. First cousins sit in the fourth degree and are free to marry. Across the Middle East and South Asia, cousin marriage is common and often preferred as a way to strengthen family ties and keep resources within the extended family.
China takes the opposite position. Article 1048 of the Chinese Civil Code prohibits marriage between lineal blood relatives and collateral blood relatives up to the third degree of kinship, which includes first cousins.6Library of Congress. When Were Marriages Between Cousins Banned in China? The ban, first introduced in the 1980 Marriage Law, was driven by public health concerns about birth defects. Any first-cousin marriage attempted in China is void from its inception.
The United States is split. California recognizes first-cousin marriages without restriction. New Hampshire lists first cousins among the relatives who may not marry each other. The patchwork creates real confusion when couples cross state lines, because a marriage valid where it was performed may not be recognized in a state that prohibits such unions. Most states that ban cousin marriage treat it as void rather than criminal, though a few add penalties.
Step, Adoptive, and In-Law Relationships
Countries diverge sharply on non-biological family. Three patterns are visible.
Some extend incest prohibitions to adoptive relationships. The United Kingdom includes adoptive parents and adopted children in its criminal incest provisions.3Legislation.gov.uk. Sexual Offences Act 2003, Section 64 – Sex With an Adult Relative: Penetration New York covers relatives “through marriage or not,” sweeping in a broader range of legal family connections.1New York State Senate. New York Penal Law 255.25 – Incest in the Third Degree
Others focus exclusively on blood. South Australia’s statute excludes relatives connected only through marriage or adoption. Canada’s provision requires the relationship to be “by blood.” A step-parent who has a sexual relationship with an adult step-child in these jurisdictions might face scrutiny under abuse or exploitation statutes, but not the incest law itself.
A third group restricts marriage between step-relatives while the underlying marriage exists, then allows the restriction to lapse once that marriage ends through divorce or death. The family bond is treated as a legal construct that can dissolve, not a permanent barrier like blood kinship.
Cross-Border Recognition and Immigration
The variation across countries creates real problems for international couples. A marriage legal where it was performed may be unrecognizable, or even criminally problematic, somewhere else.
For U.S. immigration, the State Department evaluates whether a marriage between relatives is valid using several factors. If USCIS has approved a petition with knowledge of the relationship, consular officers generally accept that determination. The underlying question is whether the marriage is consistent with the public policy of the state where the couple intends to reside. A marriage that would be void or criminal under that state’s law may not be recognized for visa purposes.7U.S. Department of State. 9 FAM 102.8 – Family-Based Relationships
That creates a practical trap. A first-cousin marriage performed legally in the United Kingdom may be recognized if the couple settles in a state that permits cousin marriage, and potentially denied if they move to one that prohibits it. The State Department has noted that applicants cannot simply establish residency in a permissive state to work around the public-policy rules of the state where they actually plan to live.7U.S. Department of State. 9 FAM 102.8 – Family-Based Relationships