Proposition 31 is a 1968 novel written by Robert Rimmer that tells the story of two middle-class, suburban California couples who turn to a polyamorous relationship to deal with their multiple infidelities as an alternative to divorce. The novel is written as a case study by a psychologist supporting a fictional "Proposition 31" that would amend the California Constitution to permit polyamory relationships. In the book, the solution to the couples' problems with adultery and the impregnation of one of the couple's wives by the other couple's husband is to commit to a group marriage to raise their five children in a home compound in which the husbands rotate among the wives. The book is a plea to pass this proposed proposition to offer a sane alternative to divorce.