Mr. Hunt is a seasoned investigator of American habits and habitats (Mental Hospital, The World of the Formerly Married, etc.). Now on the basis of advice from some 40 professionals, and a questionnaire to which 360 middle-class Americans responded, along with 91 ""in depth"" (apparently tell-all) interviews, he surveys the arrangement. Very little that is firm comes out of it except the fact that manage and monogamy are desiderata even though almost everyone, whether in fantasy or reality, diddles with the notion of extra-marital pleasures. Usually it's a question of excitement or rebellion or renewal. Those for whom it can be ""enriching"" are those to whom it is a casual bonus; the high-involvement indulgers, those whom he defines as puritan-romantics, experience guilt and anxiety which usually is self-defeating, and the affair gives way to decline and renunciation with the inevitable ""We can't go on like this."" Divorce and remarriage is a rarity (half of the remarriages fail). Interweaving these facts are the recurring case histories of some chosen couples. Even though Mr. Hunt with fair-minded liberalism pleads for a ""greater toleration of diversity"" in the years to come, one is left with the definite impression that it is better to keep off the grass which is greener. Inevitably readable, this is a kind of soap opera sociology, the latter buttressed by notes and a bibliography.