Think of the people you consider close friends—those with whom you exchange deeply personal information and emotional support, share many interests and activities, and around whom you feel comfortable and at ease (Parks & Floyd, 1996). How many come to mind? Chances are you can count them on one hand. A study surveying over one thousand individuals found that, on average, people have four close friends (Galupo, 2009).

But, what is the difference between a close friend and a best friend? Many things. First, best friends typically are same-sex rather than cross-sex (Galupo, 2009). Although we may have close cross-sex friendships, few of these relationships evolve to being a “best.” Second, best friendship involves greater intimacy, more disclosure, and deeper commitment than close friendship (Weisz & Wood, 2005). People talk more frequently and more deeply with best friends about their relationships, emotions, life events, and goals (Pennington, 2009). This holds true for both women and men. Third, people count on their best friends to listen to their problems without judging, and to “have their back”—that is, provide unconditional support (Pennington, 2009). Fourth, best friendship is distinct in the degree to which shared activities commit the friends to each other in substantial ways. For example, best friends are more likely to join clubs together, participate on intramural sports teams, become roommates, and vacation together (Becker et al., 2009).

Finally, the most important factor that distinguishes best friends is unqualified provision of identity support: behaving in ways that convey understanding, acceptance, and support for a friend’s valued social identities. Valued social identities are the aspects of your public self that you deem the most important in defining who you are—for example, musician, athlete, poet, dancer, teacher, mother, and so on. Whoever we are—and whoever we dream of being—our best friends understand us, accept us, respect us, and support us, no matter what. Imagine that a good friend tells you that he is transgendered and henceforth will be living as a woman in accordance with his true gender. How would you respond? Best friends would distinguish themselves by supporting such identity shifts even if they found them surprising. Research following friendships across a four-year time span found that more than any other factor—including amount of communication and perceived closeness—participants who initially reported high levels of identity support from a new friend were more likely to describe that person as their best friend four years later (Weisz & Wood, 2005).