Innate lymphoid cells (ILCs) are rare populations of cytokine-producing lymphocytes and are divided into three groups, namely ILC1, ILC2, and ILC3, based on the cytokines that they produce. They comprise less than 1% of lymphocytes in mucosal tissues and express no unique cell surface markers. Therefore, they can only be identified by combinations of multiple cell surface markers and further characterized by cytokine production in vitro. Thus, multicolor flow cytometry is the only reliable method to purify and characterize ILCs. Here we describe the methods for cell preparation, flow cytometric analysis, and purification of murine ILC2 and ILC3.