The present study examined friendship rules on the online social networking site Facebook. Study 1 used focus group data to inductively create a list of 36 Facebook friendship rules. Study 2 utilized survey data to examine college students’ endorsement of the various rules in close, casual, and acquaintance friendships. Results indicated five categories of Facebook friendship rules, which included rules regarding communication channels, deception and control, relational maintenance, negative consequences for the self, and negative consequences for a friend. Additionally, close friends, casual friends, and acquaintances significantly differed in their endorsement of four of the five rules categories. Results suggested that interaction rules provide a useful framework for the study of online social networking sites.