The keys to a successful, happy polyamorous relationship are up-front consent and negotiation of ground rules and boundaries, say relationship counsellors, sex educators and polyamorous couples.

BBC: Is it possible to have a happy open marriage?

"Polyamorous relationships tend to be ongoing, sustainable, emotionally bonded, committed relationships with more than one person, with the knowledge and consent of everyone involved, " says Anita Wagner, who says she has been in polyamorous relationships on and off for the last 15 years.

BBC: Is it possible to have a happy open marriage?