Innate lymphoid cells (ILCs) are lymphoid cells that do not express V(D)J-rearranged receptors and play a role in the innate immune system. ILCs are categorized into three groups with respect to their function in the immune system. ILC1 induces production of IFN-γ via T-box expressed on Tcells, ILC2 promotes production of type 2 cytokines via GATA-binding protein-3 and ILC3 promotes IL-17 and IL-22 production via retinoic acid receptor-related orphan receptor-γt. ILCs can maintain homeostasis in epithelial surfaces by responding to locally produced cytokines or direct recognition of danger patterns. Altered epithelial barrier function seems to be a key point in inappropriate activation of ILCs to promoteinflammatory and allergic responses. ILCs play an essential role in initiation and maintenance of defense against infections as well as immune-mediated diseases. In this paper, we discuss the role of ILCs in inflammatory, allergic and autoimmune diseases.