I. Criminal Prohibition of Incest in International Legal Comparison

The criminal law portion of the expert opinion commissioned by the Federal Constitutional Court is primarily intended to determine which of the legal systems under study prohibit consensual sexual activity between relatives and which do not and to examine the basis of the decision for or against criminalization. An additional issue is whether and to what extent other provisions, irrespective of the incest norm, afford protection from incestuous activity when it is committed under aggravating circumstances, such as with the use of force or within the scope of a relationship in which one of the parties exercises authority over the other or one of the parties is dependent upon the other.

These comparative legal issues were addressed by means of the functional method of comparative criminal law. The laws of 20 – ultimately of 22 – countries from a representative selection of legal systems and regions were studied. Essential to the success of this comparative legal undertaking was the choice of a comparative focus that would work as the basis of a functional legal comparison. Due to the diverse interpretations of the concept “incest” in the various legal systems, the substance of this concept could not be taken as the comparative focus; rather, the focus had to be on an appropriately constructed fact pattern. The chosen fact pattern was limited to consensual sexual activities between adult family members because the only question posed by the Court was whether there are needs for protection specific to this scenario that justify such a criminal provision (and if so, what they are). Legal provisions that criminalize sexual activities between family members only under aggravated circumstances (such as the use of force, where one of the participants is a minor, or in the case of the abuse of a relationship of authority or dependency) were not included in the comparison of “incest provisions in the narrower sense” but were the subject of a separate comparison from the perspective of whether, in the absence of an incest provision, gaps in protection could arise in such cases.

Criminal Prohibition of Incest

The results of the expert opinion show that numerous legal systems make do without a prohibition of consensual incest between adults. No such criminal provision exists in approximately one-third of the legal systems studied. The systems without criminal incest provisions include France (in accordance with the Napoleonic Code of 1811) and the legal systems influenced by French law (the Netherlands, Turkey, and the modern law of the Ivory Coast), Russia, China, Spain, Israel, and the US states of Rhode Island, New Jersey, and Michigan. There is, however, a criminal incest provision in 14 of the 22 countries included in the study: all of the Australian states and territories, Canada, Chile, Denmark, England (and Wales), Germany, Greece, Hungary, Italy, Poland, Romania, Sweden, and Switzerland as well as nearly all the states of the USA.

Grounds for the Criminal Prohibition or Non-Prohibition of Incest

Justifications for the prohibition of incest differ greatly in the various legal systems. In practice, mixed models predominate in which several grounds for prohibition are combined. Today, religious grounds no longer play much of a role at all, except in Islamic criminal law. Even moral considerations are increasingly taking a back seat and are usually only implicitly mentioned. This is because the task of criminal law in many enlightened countries is not the maintenance of morality but rather the protection of legal interests from socially harmful behavior. Occasionally, the maintenance of the incest taboo in society is also mentioned as a possible justification for prohibition; however, misgivings similar to those that arise in the context of using the criminal law to protect morality arise here as well.

Likewise, the eugenic goal of preventing the birth of “genetically defective offspring” is no longer cited anywhere as the sole justification for an incest provision; indeed, in several legal systems, eugenics is not seen as having any relevance at all. In contrast, some legal systems refer to genetic dangers as a kind of supplementary justification. These grounds are problematic, however, because the genetic risks associated with incest are not necessarily greater than other existing genetic risks, because treating the conception of handicapped children as “damage” or “harm” negates these children’s right to life, because the risk of conceiving malformed children is not punished under other factual circumstances, and because this risk can be more successfully addressed by means of education and contraception than by means of a general criminal prohibition of sexual intercourse.

In contrast, protection of the family unit is of great importance in many legal systems. This type of rationale, however, is questionable because the harm to the family unit is usually not the result but is rather the cause of the incest; it is sometimes pointed out that the traditional ideal of the family has eroded in modern times. Furthermore, a substantive analysis of the criminal norms in many legal systems also leads to contradictory results because the stated grounds for prohibition are usually not incorporated into the corresponding statutory provisions in a consistent fashion. For example, a criminal prohibition based on eugenic grounds would have to leave homosexual intercourse unpunished, while a prohibition justified on the basis of the protection of the family unit would have to include adopted children and adopted siblings.

The non-penalization of incestuous behavior is usually justified by appealing to the fact that the criminal law is not charged with the task of punishing consensual sexual activity between adults. Furthermore, the ordinary sexual offense provisions, it is said, provide adequate protection from force and abuse as well as adequate protection for minors. In addition, the claim is made that the social taboo suffices. In contrast, the decriminalization of incest in Russia and China was based primarily on ideological grounds.

Scope of the Incest Prohibition

Of those jurisdictions with an incest norm, a core group can be identified that restricts the incest prohibition to activities involving close blood relatives that could lead to procreation.

In most (nine) of these jurisdictions, the only persons capable of committing the crime of incest are thus relatives in a direct line as well as full and half-siblings. In only a few (three) countries does the pool of possible offenders include other blood relatives as well. The inclusion of relatives by adoption is not much more frequent. Only rarely are step-relatives and other relationships by marriage included within the statutory definition of incest.

Several (six) legal systems recognize only heterosexual vaginal intercourse as the act constituting the offense as described by law; incest provisions in the remaining systems include (homosexual or heterosexual) oral or anal intercourse as well. Only a few (four) legal systems also criminalize incestuous sexual activities that do not involve penetration. Interactions not defined purely in terms of sex, such as marriage or marriage-like cohabitation, are punishable only in the USA. A highly differentiated picture emerges with regard to punishment. Some of the statutory definitions for incest studied apply a single range of punishment to all offenders; in others, the applicable range depends on the relationship between the parties involved, the activity engaged in, or some other factor or factors. Maximum sentences range from a low of six months’ to a high of life imprisonment. In most of the legal systems, however, the offense is subject to a maximum of two to five years’ imprisonment.

Coverage of Incestuous Activities by Offenses with Other Protective Purposes

Because the possible negative aspects of most reported incest cases in fact consist not only in consensual sexual activities between family members but rather in additional and specific circumstances surrounding the offense, criminal provisions with protective functions other than those served by pure incest norms were also studied. The aggravating circumstances involve primarily the use of force, the young age of a participant, and situations in which one of the participants takes advantage of a relationship of authority, dependence, or trust.

A very few legal systems – including both systems with and those without a criminal prohibition of incest – provide for the possibility of aggravated punishment if an ordinary sexual offense is committed by certain family members. Regulations covering sexual activities with children or sexual activities within the framework of certain relationships of authority or dependence also function independently of provisions criminalizing consensual incest between adults. These types of offenses are never limited to perpetrators who are blood relatives; rather, a broader range of family members is included. Here it becomes clear that these norms have a different protective goal. As far as these kinds of relationships of dependence are concerned, most systems protect young people up to the age of 18 (an age that is higher than the age of consent in most systems).

Factors beyond the Criminal Law

In all countries included in the study, consensual incest is strictly taboo. Indeed, the social taboos are much broader than any existing criminal provision. They are not limited to blood relatives but cover the entire family constellation. For these reasons, incestuous couples – as well as any children born of such unions – are frequently ostracized. Nevertheless, the conclusion cannot automatically be drawn that members of such a society demand the criminal prohibition of consensual incest between adults. Furthermore, in all the legal systems studied, marriage between certain relatives is prohibited. As far as the scope of persons subject to the marriage prohibition is concerned, however, these prohibitions are extremely diverse. Thus, the incest taboo would probably exist in most societies, regardless of the presence of corresponding criminal norms and – as has been the case in France since the Enlightenment and the Napoleonic Code – would probably continue to exist without them.


The comparative legal analysis shows that a society can make do without a criminal provision prohibiting consensual sexual activities between adult relatives. In contrast, criminal norms with respect to the use of force, the young age of a participant, as well as situations in which one of the participants takes advantage of a relationship of authority, dependence, or trust are crucial. This legal comparison also clearly shows how difficult it is to find a rational justification for the criminal prohibition of consensual sexual activities between adult relatives. Hence, the issues of whether a criminal offense of incest is necessary and whether the claimed legal interests protected by such provisions should actually be recognized must first be studied more closely in the context of a criminological and genetic analysis.

  • Last update: 14 December 2017
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