Innate lymphocytes - including natural killer cells and the recently discovered innate lymphoid cells - have crucial roles during infection, tissue injury and inflammation. Innate signals regulate the activation and homeostasis of innate lymphocytes. The contribution of the adaptive immune system to the coordination of innate lymphocyte responses is less well understood. In this Opinion article, we review our current understanding of the interactions between adaptive and innate lymphocytes, and propose a model in which T cells of the adaptive immune system function as antigen-specific sensors for the activation of innate lymphocytes to amplify and instruct local immune responses. We highlight the potential roles of regulatory and helper T cells in these processes, and discuss major questions in the emerging area of crosstalk between adaptive and innate lymphocytes.