This thesis examined the rapid effects of estrogen in the medial prefrontal cortex (mPFC) on different forms of cognition, the mediating estrogen receptor(s) and possible mechanisms behind the behavioural effects. We found that ovariectomized female mice showed rapid facilitation of short-term memory in social cognition tasks, social recognition and social transmission of food preferences, but not non-social cognition tasks, object recognition or object placement. This rapid facilitation of short-term memory in social recognition task was mediated by all three known estrogen receptors, estrogen receptor alpha, estrogen receptor beta, and G protein-coupled estrogen receptor 1. However, this rapid facilitation of social cognition was likely not a result of estrogen-induced rapid local release of oxytocin in the mPFC, suggesting that other mechanisms are involved. Altogether, findings of this thesis deepened our understanding of estrogens’ rapid behavioural effects in the mPFC and expanded our knowledge of rapid estrogenic regulation of the “social brain”.