Group marriage

Also: multilateral marriage, line marriage, polyfidelitous marriage

A relationship in which three or more people consider themselves married to one another as a unit. Legally unrecognised everywhere in the West, but practised socially and symbolically by some polyfidelitous families.

1 min read · Reviewed 2026-05-24

Group marriage describes three or more people who regard themselves as married to each other collectively — not one person with multiple separate spouses (polygamy), but a single marital unit in which everyone is bound to everyone. It overlaps heavily with polyfidelity, since group marriages are usually closed to outside partners, and with the larger forms of triad and quad relationships when those partners commit at a marriage-like level.

No Western jurisdiction legally recognises a marriage of more than two people, so group marriages exist as social and symbolic commitments: shared homes, joint finances, co-parenting, commitment ceremonies, and chosen-family structures, sometimes supported by legal workarounds like cohabitation agreements, shared trusts, and powers of attorney. The legal gap is one of the practical hardships such families navigate.

The idea has a long countercultural history — the term 'line marriage' comes from Robert Heinlein's science fiction, and intentional communities have experimented with group-marriage forms for decades. In contemporary polyamory it's relatively uncommon as a formal structure but meaningful to the families who build it, and it raises real questions about legal reform that organisations advocating for relationship-structure recognition are beginning to press.

Where this term fits in the wider picture

Ethical non-monogamy is a network of overlapping practices, identities, and structures — and Group marriage connects to several of them. The neighbouring terms below show how this one sits alongside the rest of the vocabulary practitioners actually use; the guide at the end is the longer-form treatment of the same territory.

Closely-related vocabulary

Polyfidelity
A relationship structure with three or more committed partners who are not open to additional partners outside the group.
Polygamy
Marriage to more than one spouse at once — a marital and often religious institution. It is distinct from polyamory, with which it is frequently confused: polygamy is about marriage, polyamory is about loving relationships.
Quad
A four-person polycule with various internal connections — sometimes all four interconnected, sometimes a specific subset of edges.
Triad
Three people, each partnered with the other two — a complete triangle of romantic connection.
Polyfamily
A polycule that functions as a chosen family — shared household, shared finances, often shared parenting — across more than two adults.

Continue reading

The longer treatment of this territory is in the guide What is ethical non-monogamy? A clear primer for adults thinking it through — An honest, plain-language introduction to ethical non-monogamy — what it is, what it isn't, the configurations it covers, and the questions it asks of you.

New to ethical non-monogamy? Start with the glossary for vocabulary, the structures index for the named relationship configurations practitioners actually use, and the guides for longer-form treatment of the common questions.