Friendships between males and females, hereafter referred to as cross-sex friendships, are non-romantic (but not necessarily non-sexual), voluntary, non-familial relationships in which both individuals label their association as a friendship. Similar to other kinds of friendships, such as same-sex friendships, inter-racial friendships, and friendships of sexual minorities, cross-sex friendships are characterized by generic benefits in the form of mutual trust, loyalty, fun, enjoyment, and social support as well as the unique benefit of providing insider perspectives on how members of the other sex think, feel, and behave. Historically, the distinguishing characteristic of a cross-sex friendship has been that the friends are of different biological sexes and their internal gender identities match their physical bodies (i.e., cisgendered individuals). However, recent research argues for a broader definition of cross-sex friendships that includes transsexuals (Monsour and Rawlins, 2014).