The Ethical Slut by Janet W. Hardy and Dossie Easton teaches you the ins and outs of polyamory/non monogamous relationships and is a great introduction into the world of loving freely and outside of society standers! 
The Ethical Slut is written in a enjoyable, easy to understand way that will leave you with a better understanding of what polyamory really is and how you may be able to fit it in your life (if you want to). 
You can find information on communication, dealing with jealousy, and so many other aspects of relationships that can be helpful for anyone not just polyamorous people within this book. 
The Ethical Slut is inclusive of all genders, race, ethnicities, sexualities, and lifestyles and over the years has had three different edition, the content within changing with the times in order to include new idea and terminology that may not have been around when the book was first published in 1997.

After reading this book I fully understand why it's basically the bible of the poly community. It taught me so much about polyamory, relationships, sex, and even my own mind. You can definitely tell that this book was written by a therapist because all of the information given was so well researched and it gives you so much helpful advice when dealing with the struggles brought up in this book and even exercises to try. I'm definitely going to be reading the other works done by these authors!
Honestly I highly recommend this book to anyone, polyamorous or not but specifically to anyone who wants to learn more about polyamory/non monogamous relationships.