Background: One of the most influential factors shaping college students' prosocial development--the development of attitudes and behaviors that involve positive engagement within one's community and larger society--is the peer group. Friends have an especially important influence on students' learning and development because of the time and emotional investment friendship involves. While ample research documents the association between college students' friendships across racial differences and the development of prosocial attitudes and behaviors, the question of whether friendships across other social boundaries may also do so remains. Purpose: This study was guided by the theory of civic friendship, which posits that friendships that cross social boundaries (e.g., religion, race) can foster positive attitudes toward people of other social identity groups and a commitment to justice because of the solidarity and attention to injustice that develop within such relationships. We focused on friendships across the social boundary of worldview identity. More inclusive of secular and spiritual students than "religious identity," "worldview identity" is defined as a student's guiding life philosophy based on religious, spiritual, and/or non-religious perspective(s). Specifically, the purpose of our study was to examine the relationship between the number of interworldview friendships in the first year on campus and one particular prosocial attitude, pluralism orientation, which reflects acceptance of and active engagement with worldview diversity. Participants: We utilized Time 1 and Time 2 data from the Interfaith Diversity Experiences and Attitudes Longitudinal Survey (IDEALS), a national, longitudinal dataset comprised of 7,194 first-year students of diverse racial and worldview identities at 122 U.S. institutions. Research Design: We ran a series of blocked multilevel regression models to examine the relationship between the number of interworldview friendships and pluralism orientation at Time 2, controlling for four domains of variables shown in prior literature to also be associated with pluralism orientation. Results: Results revealed that, holding constant other predictors, the number of interworldview friendships in the first year on campus is positively associated with pluralism orientation. Conclusions: Our results provide additional support for the particularly powerful relationship between friendship across social differences and students' prosocial development. It is essential, therefore, that colleges and universities create conditions that will help students develop and solidify these vital relationships early in their collegiate journey. By supporting interworldview friendships among their students, colleges and universities are contributing to the creation of a more just and egalitarian society and a stronger democracy.