This is my view of the essential ethics of polyamory. I hope it can help others know what we are and are not about. I also hope this helps other polyamorous people know how polyamory does and should fit into the rest of the world.
Definition
Polyamory is the belief that having multiple loving, romantic partners at one time is morally acceptable and healthy, as long as all parties are aware of and explicitly accept it.
Some people assume that polyamory means having 3 or more partners living as a family-style unit, just like a 2-person marriage. This is one form, but polyamory can just as easily involve a married couple, with a third person involved with one or both partners, yet not living in the same house, sharing expenses, etc. That "secondary" person could, in turn, have other partners outside this relationship. They, in turn can have still more partners. The end result can be an amorphous "network" involving potentially hundreds of people, most of whom only know a few in the network.
Polyamory is often confused with "swinging". Swinging tends to be explicitly about short-term sexual relationships that tend to avoid "emotional" connections. Swingers often don't know anything about the people they have sex with and may not know whether their partners' spouses or other partners even know about their swinging. Thus, swinging often involves an accepted measure of cheating and dishonesty. This is anathema to polyamory, which demands honesty and full disclosure among partners. What's more, polyamory tends to focus on longer-term, emotional connections.
Moral Basis
Polyamory explicitly rejects the assertion that only monogamous relationships have moral standing as having no factual or other meaningful basis. The moral basis for any legitimate relationship must always be informed consent. This applies to marriage, business partnerships, etc.
Polyamorists tend to reject the notion of people as property. Most human cultures today have rejected slavery, but still define marriage in terms of property. Polyamory does not reject the legitimacy of private property (e.g., cars and houses), but it does reject the idea that getting married entitles partners to "own" one another's lives. We see relationships as always conditional and based on mutual value and respect.
Not for Everyone
Polyamory grants monogamy equal moral status. Polyamory is not appropriate for everyone, just like monogamy is not appropriate for everyone.
A polyamorous person may wish to change the minds of monogamous people about the legitimacy of polyamory. But we should never try to "convert" monogamous people who genuinely can't be poly. Nor should we assume that monogamy, per se, is bad.
Someone who is insecure about his or her own position in a relationship will probably not be willing to accept the changes that come with letting their partners seek out other relationships. Jealousy is very natural, but also anathema to polyamory. Then again, jealousy is also anathema to monogamous relationships. Trying to protect a partner as exclusive property is not a measure of a relationship's strength, but of a person's desperation to artificially maintain an unhealthy hold on someone else.
Everyone I know who is polyamorous agrees that polyamory does not make life simpler; it makes life harder. Polyamory requires enormous effort, primarily in the form of communication. People unwilling to share their desires, comfort levels, issues, and so on will find polyamory difficult at best and more likely impossible.
Culture
Polyamory advocates seek tolerance in a world where monogamy is ubiquitous and polyamory is nearly unknown.
Polyamory is compatible with monogamy. Our goal should be to see our communities, countries, and world come to reflexively accept polyamory not as a substitute for traditional, natural forms of relationships, but as one of them.
As more people become aware of polyamory, more will become tolerant. But many will lash back in a bitter and ultimately futile attempt to discredit this lifestyle. We should be prepared to be defensive, but not bitter in return. It will not serve us to dismiss monogamy as a bad thing. Better to, by example and rhetoric, to highlight polyamory as good.
Politics
Polyamorous people would like for polyamory to have equal legal standing with monogamy.
It would be tempting to seek government recognition of polyamory. Homosexuals have fought long and hard to be able to legally marry. They have won the right in some narrow contexts, but they have also managed to galvanize opposition to gay marriage.
Homosexuals probably have a better chance of gaining legal marriage status than polyamorous people will for a long time to come, which doesn't bode well for poly families seeking it.
It makes more sense to question the legitimacy of legal marriage, writ large. People who get married gain certain legal protections. Moreover, being branded an "adulterer" can bring legal jeopardy, especially with regards to custody battles for children. I think we should be seeking to eliminate or diminish all government licensure of marriage. In its place should be a branch of traditional contracting law related to marriage. Partners entering into marriage contracts should declare their assets and responsibilities and pre-negotiate arbitration mechanisms to deal with the things that typically get hammered out in bitter divorce proceedings. If no marriages are licensed, we take away the power of the majority to suppress and punish minorities.
Evangelizing
Polyamorous people may promote polyamory, but have no moral obligation to.
Polyamorous people often choose to keep their nontraditional relationships hidden from public view. This is totally acceptable. We should applaud those who chose to promote and defend polyamory, but we should never pressure others to do the same. We don't have a moral obligation to sacrifice our own lives to promote our livestyle.
Polyamorous people are slowly becoming more visible. Just giving a name to this lifestyle lends legitimacy and makes it easier for others to quickly grasp the concept. For many, it is risky to publicly acknowledge our polyamory. We can face serious repercussions from employers, family, friends, and our communities.
For those, like me, who are not yet in a position to publicly advocate polyamory, there is the Internet and other venues where we can anonymously promote it with less fear.
In this regard, polyamorous people have only one moral obligation: to not misrepresent polyamory, whether to promote, to smear, or to dishonestly profit from it. For example, getting caught cheating on your monogamous partner does not entitle you to declare you did it because you are polyamorous and so it's OK. You can't be polyamorous and cheating. If you are cheating, you are a cheater, not polyamorous.