Innate lymphoid cells (ILCs) are the most recently discovered family of innate immune cells and term “innate” means they do not need antigen receptor gene rearrangement. Due to the development of novel method, such as single cell RNA sequencing, subtypes of innate lymphoid cells are described. Based on their transcriptional profile set by main transcription factors ILCs are divided into five distinct subsets: NK cells, ILC1s, ILC2s, ILC3s, and LTi cells. ILCs are prevalent at mucosal surfaces, playing a key role in mucosal immunity and homeostasis due to their ability of rapid secretion of immunoregulatory cytokines and thus communicating with other immune cells.