I found this book at a Goodwill and picked it up, assuming it was about polyamory or swinging, as the phrase "open marriage" is generally used today. Instead I found a guidebook for loosening some of the more suffocating aspects of a traditional paired marriage while still preserving the institution.
The book starts with some easy themes, those of sharing housework and breaking out of gender roles. Hopefully not a new concept for the modern couple, even if a bit controversial for its day. It then progresses to topics such as decreasing jealousy, allowing room for self-expression within marriage, increasing communication, etc. The bulk of the book is spent on these issues, which you might find in a general relationship advice book published today. The difference is in the underlying structure and details, which hint at the better parts later in the book. The deeper message of all this is the focus on individuality and treating the couple as a synergistic pair, rather than two halves of one whole.
The last chapters are where I think Open Marriage really breaks out, and highlights some ideas that are still groundbreaking for today:
1) Takes the concept of asking for permission (your spouse "letting you do something", or having veto power over each others decisions) and trades it for discussion of goals with your spouse. Finding a 3rd alternative rather than a weak compromise in which neither party truly gets what they want.
2) Cultivating meaningful relationships outside of your family, without imposing pre-emptive limitations based on possessiveness. This is the only part where the book briefly touches upon open sexuality as a possibility for some couples, just as an example, but the main focus is on emotional depth and freedom to connect with others.
3) Commitment to real growth as an individual, and the freedom to pursue your dreams in life without having to sacrifice them to the altar of "togetherness". (And many more, but these stick in my mind most.)
Open Marriage promotes a marriage that is still monogamous and yet radically different from the way most people still conduct their relationships today. How many husbands would be happy with their wives taking a week long vacation in Europe without them? How many wives would "let" their husband go out to dinner with an ex-girlfriend? As long as scenarios like those continue to elicit fear and jealousy rather than trust and support amongst the average couple, this book will stay relevant.
(The cover's listing of authors, a husband and wife team, with their names separate rather than as "George and Nena O'Neill" was a nice touch.)