I propose a theory that puts the notion of two sexual attractions into a precise, testable form, and then I mesh it with the periodic table model of the gender transpositions described previously (Pillard&Weinrich, 1987). I define alimerentsexual attraction, active in eroticizing the physical and personality characteristics of a particular Limerent Object, and alustysexual attraction, active in producing erotic arousal when encountering a new Lusty Object. Three hypotheses then account for much of what we know about sexual orientation: (a) Limerence and lustiness are experienced by both men and women—but there is an average difference in the ease with which each can be elicited in a particular sex. Limerence is experienced by most women in our culture as an autonomously arising desire, whereas lustiness, when it occurs, is experienced mostly as a reaction to particular stimuli. Lustiness is experienced by most men in our culture as an autonomously arising desire, whereas limerence, when it occurs, is experienced mostly in reaction to particular stimuli. (b) In some people the limerent attraction can be indifferent (or nearly so) to the sex or gender of the Limerent Object. (c) The lusty attraction is rarely indifferent to the sex or gender of the Lusty Object. Individuals may vary in their readiness to respond to the two kinds of attraction. Some of this variability can be understood in the light of the periodic table model described previously, and some of it can be understood in the light of cultural conditioning and socialization. The result is a theory that deduces many of the major facts about sexual orientation from only a small number of hypotheses.