Over the past twenty-five years we have focused our efforts on understanding the mechanisms underlying this heightened responsiveness. Since we are basically psychologists we first evaluate behavior and then analyze underlying mechanisms, always keeping an eye on the behavior in question. Our approach has been to delineate the role of sensory factors, experience, hormones, and the brain in mediating the mother’s initial responses to her young as well as the long-term maintenance of her response, after the period of hormonal priming.