Polyamorous relationships exist when at least one partner in a relationship has additional partners. Consider the following hypothetical arrangement:

  • Person A is married to Person B.
  • Person B has a romantic relationship with Person C.
  • Person C is married to Person D.
  • People C and D have other partners. (They are omitted in the rest of the question for brevity).

Some states have laws against these kinds of relationships. As an example from the web, Kansas law says:

Adultery. (a) Adultery is engaging in sexual intercourse or sodomy with a person who is not married to the offender if:

(1) The offender is married; or

(2) the offender is not married and knows that the other person involved in the act is married.

(b) Adultery is a class C misdemeanor.

(Source: KSA 21-5511)

Under that law, it would seem that People B and C are likely committing adultery.

Partners in this kind of relationship are subject to certain legal risks. For example, should the relationship between C and D sour, B may be accused of adultery.

Is there any legal "thing" that can help people in polyamorous relationships protect themselves from legal risks arising from their relationships? For example, could they construct a contract or MOU which outlines their mutual expectations that they will have other partners?

  • 3
    Contracts that involve acting outside the law are void, and are not a defence against breaches of the law.
    – user4657
    Commented Nov 11, 2019 at 6:05
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    Commented Nov 11, 2019 at 15:56

2 Answers 2


I know of no laws at the federal or state level that explicitly extend their protection to poly relationships.

However, any law that purports to outlaw a polyamorous relationship among consenting adults should be looked at very skeptically, as it would likely be found unconstitutional under Lawrence v. Texas, 539 U.S. 558 (2003):

The case does involve two adults who, with full and mutual consent from each other, engaged in sexual practices common to a homosexual lifestyle. The petitioners are entitled to respect for their private lives. The State cannot demean their existence or control their destiny by making their private sexual conduct a crime. Their right to liberty under the Due Process Clause gives them the full right to engage in their conduct without intervention of the government.

While that case dealt with homosexual relationships, it seems unlikely that the courts would conclude that heterosexual couples, throuples, etc., are entitled to less protection.

Adultery laws exist in many jurisdictions, and many of them have survived constitutional challenges. But as far as I know, all those challenges relied on legal principles and precedents -- in particular, Bowers v. Hardwick, 478 U.S. 186 (1986) -- that Lawrence explicitly overruled.

In this regard, I would not expect anyone in a polyamorous relationship to encourter meaningful legal jeopardy as a result of that relationship, assuming that the relationship(s) were otherwise legal and out in the open. If A is unaware of her spouse's relationship with C, for instance, that could cause problems in a divorce proceeding.

I don't know of any legal options specifically designed for this sort of arrangement, but the more interconnected and interdependent these groups are, the more likely it becomes that some sort of written agreement would become worthwhile -- not as a response to legal danger arising from the polyamorous nature of the relationship, just to address the fact that someone is eventually going to fall short, potentially causing problems for the whole group.

There are many lawyers who specialize in LGBT issues, and I'd imagine that some of them would be able to provide more detailed advice about how to deal with this type of situation.


Except in the case that a particular relation is prohibited by law, an amourous relationship between two or more competent consenting adults is protected. The combinatorics of possible polyamorous relations is too broad to sort out exhaustively, but we can take criminal statutes against adultery as an example. In Washington, it is not a crime to commit adultery. In Idaho, it is a felony. In Massachussetts, it was a felony in 1983, and in Mass. v. Stowell it was ruled that the (former) law against adultery does not violate the fundamental right of privacy guaranteed by the Constitution. Similarly, in Texas, homosexual relations were illegal until Lawrence v. Texas, 539 U.S. 558 held that the Texas statute making it a crime for two persons of the same sex to engage in certain intimate sexual conduct violates the Due Process Clause.

The final answer depends on the specific situation you are asking about. In the case of adultery, SCOTUS has not ruled on law criminalizing it; it has ruled on laws criminalizing intercourse between persons of the same sex (ruling against such laws); it has ruled on myriad aspects of polygamy, generally holding that laws against polygamy are constitutional.

Having a contract that says "you can break the law in this manner" is no defense against criminal prosecution; it does, however, allow either party to escape the illegal consequences of an illegal contract.

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    +1. I'm not sure what your last sentence means though. What "illegal consequences" could be avoided? Commented Nov 11, 2019 at 6:17
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    For example, in a state that criminalizes adultery, you cannot make adultery legal via a contract that says "we agree to engage in an adulterous relationship". Punishment by the government is the consequence, and a contract / MOU won't change that.
    – user6726
    Commented Nov 11, 2019 at 17:21

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