So, someone you know and care about just told you that he or she is Polyamorous, or 'Poly'. Maybe it was your child, or someone else in your family. Maybe it was someone you're thinking about dating, or a co-worker, or someone you know socially.
"What?" you may have asked.
Polyamory is about being intimately involved with more than one person, openly and honestly. Poly people often use the analogy of loving children; of course you can love more than one child, and of course you can love more than one adult.
There is no one way of being polyamorous , just as there is no one way of being monogamous. Some people who are monogamous spend all of their time just with one another; others have lots of friends that they spend time with together, or separately. Some live in a nuclear family where the man is the breadwinner and controls the money, and the woman is responsible for the home and the children. Others have very independent lives and just come home to each other, or perhaps don't live together at all.
What do monogamous people have in common? They have in common that they have agreed with their partners that they will only be romantically and sexually  involved with one another. Poly people have in common that they have agreed that they may be romantically and sexually involved with more than one person, and will be honest and open  about those relationships. Poly people can be straight, gay, lesbian, bisexual, trans, etc., just as monogamous people can be.
Poly is not cheating.  Cheating involves breaking an agreement with your partner about who you can be romantically and sexually involved with. In a poly situation, who you can be romantically and sexually involved with is something that partners talk about, agree and consent to.
Some poly people have relationships involving more than two people, but are not open to additional partners. (e.g., three people may all be involved with one another, but not with anyone else) That's often called "polyfidelity." On the opposite end of the spectrum, there are people who have many casual sexual involvements. That can be called a number of different things; some of those folks consider themselves (or are considered by others to be) "swingers" ; some consider themselves poly and happily promiscuous; some consider themselves monogamous and dating around!
Most poly folks fall between those extremes. They balance relationships that may be serious and committed, emotionally involved but not seriously committed, or more casual. Given the limited hours in a day, most poly folks find that they can only maintain a few serious relationships. Less serious relationship tend to take less time, and therefore people may be able to be involved in more of those. Sometimes these relationships are consciously organized in a very hierarchical way, and sometimes not at all.
Some poly folks are married by law or in spirit, and some have made life-commitments to more than one of their partners.  In most cases, a poly person who is married will have an agreement with his or her spouse to make their marriage "primary". This is especially true for those with children. Like most parents everywhere, most poly parents put highest priority on their children.
People are poly for many reasons and come to polyamory from many different angles. Some start out in monogamous relationships, cheat with painful results, and come to polyamory as a way to handle their attraction to multiple people in a negotiated and consensual way. Others read about open non-monogamy in fictional books or on the web, and find it resonates with them. Some may be attracted to someone who is poly, and learn about it from that person, and decide it is something they want to try.
People in monogamous relationships sometimes open those relationships up. Especially in those cases, people are usually very careful to protect the existing relationship, and often negotiate limits and make agreements to move things slowly in order to prioritize and maintain their existing relationship as "primary". Some couples worry that opening their marriage will hurt their relationship, but with care most find that their relationship stays essentially the same, or improves.
Those negotiations can be especially important to keep stability in the family for children, always a high priority for parents. Parents have different ways of talking to their kids about their other partners, based on the children's age and personality, how in or out of 'the closet' the parents are, and how big a role the other partners play in the kids' lives. It may also vary based on geography or the social environment; in some areas it may be very important that the children not know or not talk about their parents' relationships, while in other environments it may not be any stranger than children who have two mothers or two fathers.
People in decades-long poly relationships  have developed many skills for communicating with their partners and handling the myriad logistical and emotional complications of balancing relationships and making sure that all involved are getting what they need. We've been lucky that several of those folks have agreed to write for our site, or allow us to link to their writing elsewhere, and we welcome you to read further.
 Some people identify as *being* polyamorous, and some people think of it as something that they *do*. For sake of this discussion, we'll let that distinction be blurred. back
 Sometimes the romantic and the sexual do not go together. Monogamous people sometimes have only agreed to be sexually involved with one another but made no agreements about romantic or emotional involvements. Sometimes people who are polyamorous have agreed to be sexually involved with other people but not romantically involved with other people. For the sake of this discussion, we'll leave out those cases. back
 One arrangement of polyamory is called "Don't Ask Don't Tell" – the partners have agreed that one or both of them may have outside sexual or romantic involvement, but that they will not tell each other anything about those involvements. back
 It is certainly possible to cheat within a poly relationship. People often have agreements about the circumstances under which it is ok to get involved with someone new, or who it is ok to get involved with, and breaking those agreements can certainly be considered cheating. back
 There is much debate to be had across many online poly communities, on poly vs swinging. Personally, I think the difference is much more one of subculture than of behaviour. back
 "Mormon polygamy" (which is of course not condoned by the LDS church) sometimes bears more than a passing resemblance to polyamory on the surface. It is distinguished in that only men may have more than one spouse, it comes from a religiously-based belief that is not held by most that practice polyamory, and is often quite patriarchal. back
 Yes, there are many people in very long term polyamorous relationships. back