Our discussion has focused on a set of behavioral and physiological factors which influence fecundability. Some potentially important determinants are notable primarily because of their absence. Foremost among these determinants (as a group) are the male attributes. We have, by and large, ignored the links between male sexual behavior and hormonal profiles and the effects of hormones (or other factors) on sperm function. The fact that we have not reviewed them here does not imply that we believe that they are unimportant. Indeed, the effects of male factors may be particularly important because in some settings men are the predominant, if not the sole, decision-makers regarding reproductive behaviors including initiation of sexual intercourse and use of contraception. Also conspicuous by their absence are the effects of nutrition, consumption of alcohol, exercise, smoking, and behavioral and hormonal correlates of stress, all of which may affect fecundability. We have, though, reviewed a wide range of factors which contribute to fecundability and identified several points of potential interaction between the behavioral and biological determinants. We expect that our future understanding of these processes will be enhanced by empirical work and modeling efforts which also interact to draw upon the insights provided by each.