Not everyone in American society believes monogamy is the best way of life. Many people are polygamous or polyandrous, and some are polyamorous. Polyamory comes from the Greek prefix poly meaning "many" and the Latin word amor meaning "love." Polyamory thus means having many loves. While some religions perceive this as sinful, most people who practice polyamory are pagan. I am polyamorous.
The greatest advantage of polyamory is always being able to go out with someone new. If you meet an interesting person, there is nothing stopping you from going out with him or her. But there are so many things to love about dating several people. The next important motive, to me at any rate, is always having someone to talk to or spend time with. Also, no matter what mood you might be in, there will always be someone who understands and caters to that mood better than others. Finally, if you need help, you don't have to wait for one person to become available; there is most likely someone else who can help you.
The greatest disadvantage of polyamory is scheduling. Having to cooperate your schedule with those of several other people can get very difficult. Having a memory as horrid as I do only makes it worse, and I have problems just scheduling friends! If one person has limited time available for you, it makes it hard for you to set aside that specific time for him or her. There is also the problem of overbooking. As a person who doesn't use a date book myself, I recommend you get one, especially if you're going to have several partners. Rescheduling can be a hassle. Scheduling in the first place can be a hassle sometimes.
There is one single important rule in polyamory: keep relationships separate! Even though you may have several relationships, that does not excuse you from putting any less effort into it than if you had only a single relationship. Keeping relationships separate allows you to put the proper effort into any single relationship without mixing up or offending partners, and a relationship may progress naturally without avoidable outside interference. Some people do this by dating people from different social groups, some by dating people in different areas, and others by devoting periods of time to specific partners (for example, a week with one and then a week with another). I encourage others to follow this rule enthusiastically because you should date someone for his or her own merits, not for being able to say that you're dating so many people.
Polyamory also provides for multiple person relationships. I have no experience in this area personally, and I have not talked to anyone about it who has that experience. In theory, though, there could be more than two people in a relationship, and I have heard several times that such relationships exist.
Polyamory may not suit everyone. Some people will never accept an idea so foreign and taboo, especially when they perceive it as sinful. Some simply cannot handle having more than one romantic partner. For those of us who practice polyamory, though, it can often be a very fulfilling and continually exciting experience.
This is based on a paper I wrote for English, so excuse how the tone of it hardly fits the format. (I think they don't match, anyway).