Teams and groups are central to our lives, both professionally and personally. This chapter explores the duality of humor in teams: its ability to unite and divide. Four processes explain how humor impacts team social outcomes by reinforcing affect, increasing perceived similarity, enhancing self-disclosure, and highlighting hierarchical salience. Examining the development of laughter and humor in our hominid ancestors can deepen our understanding of interpersonal humor effects. Laughter serves as an acoustic signal indicating a safe environment and helps spread positive affect among group members. Current research based on evolutionary theory investigates the spread of positive affect in work teams, the size of natural laughter groups, and fake laughter. A microlevel analysis of specific humorous comments also reflects the duality of humor. The chapter concludes with a note of caution, future research ideas, and practical implications.