Age: Middle aged, or at least over 30.
"Usually guys have to be older to get over the jealousy issues that can come with swinging," says Philip Moore spokesman for Irishswingers.ie
"Younger people are coming, through, but they aren't popular with established swingers who don't want to be compared to the bodies of 20-somethings."
Most are middle class. "Swingers like to be able to talk on the same level as each other," says Moore. "It's not just about sex, there needs to be an intellectual attraction."
How to find them
Ankle bracelets are becoming common among members in Ireland, while Pampas grass outside homes is the calling card of swingers in the UK.
Otherwise most meet online on dedicated websites.
No always means no. Wives talk to each other as soon as possible to establish that they are dealing with a genuine couple before meeting up. Voyeurism is frowned upon.
Will it work for you?
"You have to have a very good relationship to be able to watch your wife be intimate with someone else," says Moore. "But if you're doing it within the confines of a loving relationship, swinging can work." He adds: "Anyway, it's like bungee jumping, if you decide to do it and don't like it, just don't do it again."