I could quote passages from that at the bisexual discussion group I often facilitate to good effect, and I suspect I'll be doing just that in the future. Although this book is not about polyamory directly, polyamory does involve a lot of radical truth-telling, and this book is common in parts of the poly community. Whether or not you tell the truth is. The breadth of her references almost seem to prove the timelessness of many of her points. There are a lot of gems here.
Marriage is truly a landmark book.
The main point of this book is that a truly successful, fully actualized marriage requires a relationship in which each partner has a sense of individual identity, isn't constrained by the social patterning of standard gender roles, may want a certain amount of privacy, and so on. Independence, and mutual respect for each others independence, form a basis for a trusting relationship of equals, which promotes trust and emotional intimacy. And, as more of a logical consequence than a central point, they suggest that relationships can go on to allow the people in it to have other loving and or even sexual partners in some cases. The O'Neills saw, as I do, loving other people outside of a primary relationship as an extension of the natural evolution of relationships. All and all, an excellent book well worth reading for polyamorous and monogamous people alike.