Organisms do not live their lives alone, but in constant interaction with other organisms. Despite widespread imagery of “nature red in tooth and claw,” many of these interactions are mutually beneficial. The question of how such interactions arise and persist in nature has long challenged Western biologists, and engaging with this topic can deepen our understandings of ecology, evolution, and human beings’ own interactions with other organisms. In this course, focused on close reading and discussion of scientific literature, we will explore the biology underlying a diverse set of mutualistic interactions, consider several efforts to understand them from theoretical perspectives, and investigate how they are responding to anthropogenic global change.