Interleukin-1 family 7 (IL-1F7) is a novel member of IL-1F cytokines. IL-1F7 is more commonly known as IL-37. IL-37 can join the α-subunit of the IL-18 receptor, or IL-18 binding protein (IL-18BP), and binding of these proteins can enhance the IL-18 suppression. IL-37 also translocates to the cell nucleus and affects gene transcription. IL-37 inhibits the phosphorylation of p38 mitogen-activated protein kinases. Almost all reports showed that IL-37 has remarkable anti-inflammatory activity. IL-37 plays an important role in a variety of inflammatory and autoimmune diseases, as well. Recently, studies demonstrated that the expression of IL-37 is abnormal in many diseases such as inflammatory bowel diseases, inflammatory respiratory diseases, atherosclerosis, hepatitis, obesity, contact hypersensitivity, Graves' disease, rheumatoid arthritis, ankylosing spondylitis, systemic lupus erythematosus, multiple sclerosis, psoriasis, and Behcet's disease. Here, we will review the biological characteristics of IL-37 and its key roles in various inflammatory and autoimmune diseases.