Animals inhabiting temperate environments have evolved mechanisms to interpret environmental cues and adjust their behavior and physiology in order to maximize survival and reproductive success. Reproduction is an energetically costly process that is inhibited in the winter in seasonal breeders to conserve energy when the chances of successful reproduction are minimal. Seasonally breeding rodents serve as an ideal model system to investigate the neural control of the reproductive axis in a controlled laboratory setting, as surgical and pharmacological methods of reproductive axis inhibition are not required. The aim of the present series of experiments was to elucidate how the brain processes information about the length of the day in order to communicate time of year to the reproductive axis to coordinate reproductive function and behavior. Specifically, the studies herein aimed to investigate the role that two novel neuropeptides, kisspeptin and gonadotropin-inhibiting hormone (GnIH or RFRP in mammals) serve in processing and communicating day length information to the reproductive axis in several species of seasonally breeding rodents. The results uncover important roles for these two neuropeptides in the interpretation of photoperiodic signals for regulating the process of gonadal regression in response to the short day lengths typical of winter in these species. Additionally, by exploiting natural genetic variability within populations of seasonal breeders, these studies suggest that the phenomenon of nonresponsiveness and phenotypic variation in reproductive photoresponse may result, at least in part, from variation in the morphological features and seasonal response of the RFRP system. As a whole, this body of work provides important insight into the complex neural mechanisms that have evolved for integrating environmental information in order to coordinate reproductive physiology with a changing external environment.