beta-Glucans are naturally occurring carbohydrates that possess immune-modulating activities, but their mechanisms of action are largely unknown. Recent discoveries, however, including identification of beta-glucan receptors, such as dectin-1, have started to shed some light on the mechanisms underlying the properties of these carbohydrates. The characterization of dectin-1, in particular, has revealed some of the processes involved in beta-glucan sensing, intracellular signaling, and induction of cellular responses and has provided new insights into the role of beta-glucans in immunity and disease. Here we review both beta-glucans and their receptor, dectin-1.