Is polyamory legal?
Yes, with caveats. Having multiple romantic or sexual partners simultaneously is legal almost everywhere; legally marrying more than one person at a time is not. A handful of US jurisdictions have begun recognising multi-partner domestic-partnership structures. Custody, employment, and housing protections remain inconsistent.
The basic legal landscape, in the US and most peer democracies, is that adults are free to have whatever relationships they choose to have with consenting other adults. Polyamory in the everyday sense — multiple loving partners, with everyone's knowledge — is not regulated, not prohibited, and not subject to direct legal consequence in itself.
What is regulated is legal marriage. Most jurisdictions legally recognise only one marriage at a time per person; entering a second legal marriage while still legally married to the first is bigamy. This is the source of common confusion: 'polyamory is illegal' usually conflates legally-recognised polygamous marriage (which is restricted) with polyamorous relationship practice (which is not).
A few US municipalities have begun recognising domestic-partnership structures with more than two participants — Somerville, Cambridge, and Arlington in Massachusetts, Berkeley and Oakland in California, among others. These ordinances grant some of the local recognition benefits (hospital visitation, family-leave eligibility) without overriding state or federal marriage law.
Where polyamorous people commonly do encounter legal friction: child custody (a parent's polyamorous structure can be raised against them in divorce proceedings, though appellate courts have been increasingly unwilling to penalise structure absent demonstrable harm to the child), employment (no federal protection against polyamory-based discrimination in most jurisdictions; some local protections exist), housing (occupancy ordinances often limit unrelated adults sharing a residence), and immigration (only one spouse can be sponsored).
Practical workarounds for the legal-recognition gap include: explicit cohabitation agreements, healthcare proxies, durable powers of attorney, beneficiary designations, and clear estate planning. None of these fully replicate marriage but they cover most of the practical infrastructure that polyamorous households need. Speak to a family-law specialist in your jurisdiction.