Open marriage is a form of non-monogamy in which the partners of a dyadic marriage agree that each may engage in extramarital sexual relationships, without this being regarded by them as infidelity, and consider or establish an open relationship despite the implied monogamy of marriage. There are variant forms of open marriage such as swinging and polyamory, each with the partners having varying levels of input into their spouse's activities. Terminology A general definition of an open marriage is that there is an agreement between the two partners to have some degree of sexual interaction outside the couple. There are variant forms of open marriage, each with the partners having varying levels of input on their spouse's activities. The term open marriage originated in sociology and anthropology. Through the 1960s, researchers used "closed marriage" to indicate the practices of communities and cultures where individuals were intended to marry based upon social conventions and proscriptions, and open marriage where individuals had the ability to make their own choice of spouse. Nena O'Neill and George O'Neill changed the meaning of the term with the 1972 publication of their book Open Marriage. The O'Neills describe open marriage as a relationship in which each partner has room for personal growth and can individually develop outside friendships, rather than focus obsessively on their couplehood and their family unit (being "closed"). Most of the book describes approaches to revitalizing marriage in areas of trust, role flexibility, communication, identity, and equality. Chapter 16, entitled "Love Without Jealousy", devoted 20 pages to the proposition that an open marriage might possibly include some forms of sexuality with other partners. Fueled by frequent appearances of the O'Neills on television and in magazine articles, the redefinition entered popular consciousness, and open marriage became a synonym for sexually non-monogamous marriage. In her 1977 book The Marriage Premise, Nena O'Neill advocated sexual fidelity in a chapter of that name. As she later said, "The whole area of extramarital sex is touchy. I don't think we ever saw it as a concept for the majority, and certainly it has not proved to be." Definitional issues The meaning of open marriage can vary from study to study depending on how the particular researchers have set their selection criteria. Individuals might claim to have open marriages when their spouses would not agree. Studies and articles that interview individuals without taking their married status into account may