Hormones facilitate the coordination of social and cognitive processes which are fundamental to life by exerting synergistic effects on individuals’ physiology and behavior. In this dissertation, I use the model of the human female’s menstrual cycle to examine how endogenous fluctuations in circulating hormones are related to changes in both an individual’s social behaviors and perceptions and those of their conspecifics. When women are in the most probabilistically fertile phase of their menstrual cycle, they tend to exhibit behavior characteristic of status competition with other women. Analogous motivations among probabilistically fertile women may put fertile-phase women in direct competition with each another. In three studies, I test the hypothesis that women are more vigilant towards fertile-phase women, particularly when they are in the fertile-phase of their own menstrual cycle, based on visual cues to other women’s fertility. In Study 1, I demonstrate that women behaviorally distinguish between fertile- and non-fertile-phase women as a function of their own fertility status, such that probabilistically fertile women give fewer resources to other fertile-phase women. In Study 2, I demonstrate that women attend to fertile-phase women more than non-fertile-phase women and, when they are in the fertile-phase of their own cycle, are slower to indicate that a fertile-phase woman matches one held in memory. These effects are observed only when women have low visual working memory, which is related to increased susceptibility to attentional capture. In Study 3, I find evidence that women differentially attend to some features of fertile- and non-fertile-phase women’s neutral faces, but not features associated with emotional expressivity which typically conveys threat. Taken together, this work extends previous research which has demonstrated that women engage in greater intrasexual competition when they are probabilistically fertile by considering women’s sensitivities to other women’s hormonal and associated motivational states. I discuss this work in the context of hormones’ coordination of physiological and behavioral responses to changing fitness demands.