Open relationship

An open relationship is one where the partners agree that sex, and sometimes romance, with other people is allowed. It is one form of ethical non-monogamy. In a 2012 US survey of 2,270 partnered adults, 4% said they were in one. The studies we read find similar satisfaction on average, and lower functioning in one-sided arrangements.

Updated October 6, 2026

Means

A couple that agrees sex with other people is allowed

First seen

'Open marriage' in the sense used today from the early 1970s (the O'Neills' 1972 book; Merriam-Webster dates the phrase to 1971); 'open relationship' earlier meant a relationship with few secrets, per Dictionary.com; 'monogamish' popularized by Dan Savage in 2011

Related terms

ENM (ethical non-monogamy), Friends with benefits (FWB), Casual dating, DTR (define the relationship), Situationship

In Swedish

Öppet förhållande

An open relationship is a couple’s agreement that sex with other people is allowed, and it is one form of ethical non-monogamy, or ENM. In the studies we read, couples in one look about as satisfied on average as monogamous couples; the partially open and one-sided arrangements showed lower functioning. We take no side on opening a relationship or keeping it closed.

What it means to be in an open relationship

Dictionary.com’s slang entry, dated March 1, 2018, describes a relationship “where an established couple has mutually agreed to share a non-monogamous lifestyle.” The phrase once meant something tamer: “any type of relationship that had open communication and few secrets.” The entry credits the current sense to George and Nena O’Neill’s 1972 book Open Marriage (Dictionary.com, 2018).

Merriam-Webster dates “open marriage” to 1971, a year before the O’Neills’ book, and defines it as “a marriage in which the partners agree to let each other have sexual partners outside the marriage” (Merriam-Webster). Writing in The Believer in 2014, Nick Hornby noted that the book spent 40 weeks on the New York Times best-seller list and that 3 of its 287 pages deal with monogamy. “We are not recommending outside sex,” the O’Neills wrote, as Hornby quotes them, while “not saying that it should be avoided, either” (Hornby, 2014). That is a lot of title for three pages.

For a married couple, the name is open marriage. Another word, monogamish, is Dan Savage’s term, popularized in 2011 (Oppenheimer, 2011). In research it is narrower: relationships that “restrict sex outside the relationship to instances in which both members of the couple participate together” (Parsons et al., 2013, read in Starks et al., 2018).

The count we lean on is the 2012 National Survey of Sexual Health and Behavior, a US probability sample, which asked whether a relationship was “open (meaning that you and your partner have agreed that one or both of you can engage in sexual activities with other people)”. Of 2,270 people in a relationship, 4% reported an open one, 89% monogamy and 8% nonconsensual nonmonogamy. The authors flag their “reliance on one survey item, which had not been subjected to validity testing” (Levine et al., 2018).

How does an open relationship work? The rules couples set

It works by agreement, and the agreements get specific. The table collects some reported in studies and in threads on Mumsnet, a British parenting forum. They describe what couples said they do; none of them is a recommendation.

Agreements couples report, and where we found them

Agreements are common among people who answer surveys about them. In a 2023 study of 722 US participants, 83.7% of them non-heterosexual, 594 (82.3%) “had a relationship agreement.” Having one “regardless of the type” went with higher satisfaction (Vilkin & Davila, 2023).

Hoff and colleagues recruited 566 gay couples in the San Francisco Bay Area between June 2005 and February 2007. “Ninety nine percent of couples reported having an agreement.” Eight percent “reported discrepant agreements” (Hoff et al., 2010), meaning the two partners named different ones. Some couples do not agree on what they agreed.

Open relationship vs polyamory, and ENM

An open relationship usually opens sex. Polyamory opens love: more than one romantic relationship at a time, with everyone aware of the others. ENM is the umbrella over both, along with swinging and other set-ups, and the full table is under types of ENM. Surveys draw the line in different places: the 2012 item above says sexual activities, while YouGov’s 2023 definition says “sexual or romantic relationships” (YouGov, 2023).

Our rule of thumb: count the relationships that matter to the people in them. One couple with agreed outside sex is an open relationship; a second relationship that matters to someone is nearer polyamory.

Two single people in an FWB arrangement are not in an open relationship, since there is no relationship to open, and most casual dating is not exclusive to begin with.

Is an open relationship healthy? What the research says

Approval and well-being are separate questions, and the surveys below answer only the first.

In a YouGov poll of 1,000 US adult citizens on its opt-in panel, February 1 to 6, 2023 (margin ±3.4%), 12% strongly and 20% somewhat approved of open relationships, while 18% somewhat and 40% strongly disapproved. On a scale from 0, completely monogamous, to 6, completely non-monogamous, 55% put their ideal at 0 and 8% at 6 (YouGov, 2023). A third put their ideal somewhere other than 0. The 2016, 2020 and 2021 YouGov polls are tabled on ENM.

Pew asked 5,073 US adults in April 2023 about “a marriage where both spouses agree that they can date or have sex with other people.” A third found it acceptable (23% completely, 11% somewhat) and 50% unacceptable. Acceptance ran from 51% of adults under 30 to 15% of those 65 and older (Pew Research Center, 2023).

In a 2017 online survey of 2,003 Canadian adults, 4.0% of those in a relationship were currently in an open one (Fairbrother et al., 2019). Two surveys in two countries, five years apart, put it at about 4%. Lifetime figures for single Americans are under can you cheat in an open relationship. We found no UK or Swedish figure.

The well-being studies used self-selected or convenience samples, mostly measured once, so they show what went together, not what opening does to a couple. On average they find little difference. The abstract of Conley and colleagues’ 2017 review and study, which we read as a search extract, reports few differences in relationship functioning between monogamous people and people in consensual non-monogamy (CNM, the research term for ENM) in online convenience samples (Conley et al., 2017). We read that as similar on the measures used. Wood and colleagues compared 348 people recruited on Amazon’s Mechanical Turk, 142 consensually non-monogamous and 206 monogamous, and found “No differences in mean levels of relationship and sexual satisfaction” (Wood et al., 2018).

Hangen, Crasta and Rogge sorted 1,658 online respondents, about 70% of them women and mostly in their 20s and 30s, into five groups: monogamous at an earlier and a later stage, consensually non-monogamous, partially open, and one-sided (ScienceDaily, 2019). From the abstract: “the monogamous and CNM groups demonstrated high levels of relationship and individual functioning, whereas the partially-open and one-sided nonmonogamous groups demonstrated lower functioning” (Hangen et al., 2020). Our reading: what separated the groups was whether both people had agreed.

Murphy, Joel and Muise followed, for two months, 233 people who were planning to open their relationships. The 155 who did “experienced significant increases in sexual satisfaction,” and the authors “found no evidence that engaging in CNM impacted either life satisfaction or relationship quality with the primary partner” (Murphy et al., 2020). Our caveats: they were already planning it, they picked themselves, and two months is short.

When a partner asks to open the relationship: what to do about it

These steps are ours, and they apply whoever is asking.

1. You do not have to answer the same evening. The request changes what the two of you agreed, and that can take more than one conversation. One of ours, not tested at scale: “I’m not answering tonight. You’ll have my answer by the weekend.”
2. Ask what they want opened: sex, or more. On The Student Room, a UK student forum, a thread started February 15, 2023 (14 replies) came from someone whose girlfriend had asked. One reply: “Have you asked her why she wants one?” (The Student Room, February 2023).
3. Say so if only one of you wants it. In the Hangen study above, partially open and one-sided arrangements went with lower functioning. Another reply in the same thread said “one person pushing for an open relationship when the other is reluctant will be a recipe for disater” (sic) (The Student Room, February 2023). In the July 2023 Mumsnet thread, a reply said “anyone who goes into one because of pressure or fear of losing the other or because they don’t feel sexually ‘enough’ is just going to become miserable” (Mumsnet, July 2023).
4. Agree what counts, and when you will look at it again. Breaking the terms is still cheating in an open relationship, and the conversation works like a DTR with different questions. In the October 2014 Mumsnet thread, one poster was “together 17 years, married 13. Open for about the last 7 or 8. Happy.” The same poster wrote: “Setting ‘rules’ up front is very important.” Another, together 41 years, had had “an open marriage for years which both of us readily agreed to” (Mumsnet, October 2014).
5. Either of you can close it again. In a Mumsnet thread started November 29, 2022 (about 29 replies), from a married woman dating women with her husband’s consent, a reply said: “ENM isn’t a one way decision. You can change your mind, take a break, whenever it’s needed, or for good, if that’s for the best” (Mumsnet, December 2022).

The replies we quoted go different ways on whether it works at all; we did not count replies by theme. In a Mumsnet thread started August 6, 2022 (about 44 replies), one reply said “If both of you would be happy with that scenario then give it a try.” A reply the next day: “Opening a relationship means bringing more emotions and more complications” (Mumsnet, August 2022). In a Student Room thread started December 17, 2022 (8 replies), one reply’s conditions included being “always honest with themselves & each other” (The Student Room, December 2022).

If the request comes with threats, fear or one partner controlling the other, that is a different conversation; the helplines are in the last step on our red flags page.