Find out what books are popular for learning about polyamory. I'll tell you who should read them based on your situation.
Everyone! Covers the basics of polyamory and goes in depth on relationship styles, agreements, jealousy, and more. It's the book I wish I'd read when I started my poly journey, if it had existed back then.
Everyone! Dr. Sheff is the premier researcher on polyamory and presents an in-depth view of the ways people practice polyamory. She admits she did not get enough voices from people of color--maybe the next edition?
Science minded folks who want to prove that nonmonogamy has been common all along. The authors take an anthropological view of human relationships and assert that the modern view of marriage is unnatural.
Your mono family and friends. This is a short volume that explains the basics of polyamory and hopefully encourages a longer conversation about how and why you chose to be nonmonogamous.
Couples looking to explore together. This book goes over the basic forms of nonmonogamy and offers tips specifically for couples already involved.
Baby boomers. This book was revolutionary when the first edition came out, but anyone born after the birth of MTV will find it underwhelming and obvious. It's required reading if only to learn how far we've come.
Poly and queer lovers. Tikva Wolf is a delightful cartoonist and her comics give an overview of all the aspects of polyamory with funny and realistic characters.