Objective. Previous studies have examined interracial friendships, typically within educational settings, in relation to racial prejudice without taking in to account the formation of interracial friendship. I address the void in the literature regarding the presence and formation of adult interracial friendship formation using four racial hierarchy theories: bi-racial divide (White/non-White and Black/non-Black), the tri-racial divide, and the melting pot. Hypotheses regarding friendship selection and formation are derived from the four racial theories. Methods. Using the Portraits of American Life Study from 2006 (n=2610) and 2012 (n=1314), I conduct multivariate analyses to test my hypotheses. Results. Adult interracial friendships are quite rare and those that do form rarely survived during the six years period between surveys. For the brief time that adult interracial friendships are established, they often develop within the tri-racial structure. Whites are the least likely to engage in interracial friendship, while racial minorities are more likely to engage in interracial friendships with Whites. Additionally, those of medium skin tone have higher proportions of interracial friendships than those of lighter or darker skin complexion. Finally, except for blacks, respondents in tracts with higher levels of racial homogeneity are less likely to name a friend of a different race. Conclusions. The decreasing and unstable nature of interracial friendship composition is problematic because it inhibits bridging capital, that is, the ability for racial equality to occur through the passing of social capital between racial groups.