Friendships have a bigger effect on our psychological health and wellbeing, as well as our physical health and wellbeing, than anything else. Friendships are, however, extremely expensive to create and to maintain, both in terms of their time cost and in terms of their underpinning neurobiology.  The basis of this lies in the endorphin system and the way this is triggered by physical touch acting through the afferent C-tactile neural system. In this lecture, I’ll explore the behavioral, cognitive and neurobiological bases of friendships