Tennov's central argument, illustrated with accounts from individual experiences, is that there is a well defined and involuntary state "limerence" (a term chosen to avoid the confusion surrounding "love"), roughly equating with "being in love". Key features include obsessive thinking about the limerent object, irrationally positive evaluation of their attributes, emotional dependency, and longing for reciprocation. Not all people experience limerence, but it is a normal and non-pathological condition. The negative side of limerence is apparent in the effects of unrequited limerence and the problems limerent behaviour can pose the non-limerent.
Tennov goes on to look at limerence more broadly, again using accounts of personal experiences. Socially it has widespread effects, most dramatically in marriage and youth suicide. Limerence has received generally negative press from psychologists and philosophers and Tennov briefly surveys some of the writing on the subject (though she doesn't attempt any kind of literary history, despite using quotes from literature). Tennov finds surprisingly few differences between the sexes in limerence; she also suggests that polarity may be more clear-cut with limerence than with sexual attraction.
Despite taking a broad approach, Tennov skims over some obvious questions. Is limerence really cross-cultural? Almost all of the personal accounts offered are from the United States and all we are given no evidence for generalisation (apart from a stray comment about love magic being universal). What biological basis is there for limerence? All we are offered is some fairly naive sociobiology (no doubt reflecting the late 70s date). But Tennov acknowledges the limitations of Love and Limerence herself, concluding with suggestions for research and writing "This is a preliminary report. Its purpose is to open a field for investigation". Given that love and limerence have become more respectable topics for serious enquiry, however, Love and Limerence really needs to be updated to reflect work done in the last twenty years.
It won't be of much benefit to the unhappily limerent, but Love and Limerence may contribute to both individual understanding and social policy. It can also be read simply as entertainment.