In many species of rodents, sense of smell is the most important source of information about the social and nonsocial world. I selectively review the literature on chemical communication in this group, primarily as studied in the laboratory. I start with a discussion of the term “pheromone,” the types of chemical signals, and the mechanisms underlying responses to chemical signals. I discuss the chemical complexity of odors in rodents and the significance of multiple sources of odors. Efforts to chemically identify signals are reviewed briefly; some progress, especially with domestic house mice (Mus musculus domesticus), has been made, but new collaborations between chemists and biologists are needed. Three areas of current research are reviewed in detail: the role of the major histocompatibility complex in the production of body odors and the role of these odors in mate choice, the use of odors in kin recognition, and the functions of scent overmarking.