DescriptionThe power of word-of-mouth (WOM) lies in its ability to influence consumer behavior and purchase intention, highlighting drivers of WOM behaviors that are critical to marketers. This dissertation examines a biological factor that influences women’s desire to engage in WOM—monthly ovulatory cycles. Estrogen is a hormone that increases near ovulation, regulates women’s fertility, and shifts women’s social motives and behaviors. This study tests whether fertility influences women’s desire to engage in WOM with others. Six studies suggest that women demonstrate greater desire to share information at high fertility—near ovulation. However, the fertility-regulated increase in the desire to share information was specific to sharing only with other women, an effect that emerged in both hypothetical and real social network behaviors. Additional findings corroborate the prediction that product type moderates the relationship and that sharing information during high fertility functions partially to build alliances with other women and mitigate mate competition. These findings have important implications for understanding how hormones that regulate fertility influence women’s desire to share information, including mating motives that underlie the effect.