A major tenet of attachment theory is that the stability of the caregiving environment drives the stability of infant attachment security. The research investigating the factors related to the stability and change of infant attachment is limited by its lack attention to infant characteristics related to attachment stability outcomes. The newly developed differential susceptibility hypothesis posits that temperamentally difficult children are more influenced by their caregiving environment. In the present study, I examine infant irritability as a moderator of the link between changes in maternal (a) depressive symptomatology, (b) life satisfaction, and (c) parenting self-efficacy on changes in infant attachment security between 12 and 18 months.