T helper type 2 (T_H2)-mediated immune responses are induced after infection with multicellular parasites and can be triggered by a variety of allergens. The mechanisms of induction and the antigen-presenting cells involved in the activation of T_H2 responses remain poorly defined, and the innate immune sensing pathways activated by parasites and allergens are largely unknown. Basophils are required for the in vivo induction of T_H2 responses by protease allergens. Here we show that basophils also function as antigen-presenting cells. We show that although dendritic cells were dispensable for allergen-induced activation of T_H2 responses in vitro and in vivo, antigen presentation by basophils was necessary and sufficient for this. Thus, basophils function as antigen-presenting cells for T_H2 differentiation in response to protease allergens.