 The Janus kinase, JAK, signal transducer and activator of transcription, STAT, pathway is an important signal in cascade that plays a critical role in cellular communication and regulation of many biological processes. It is involved in the regulation of cell proliferation, differentiation, metabolism, and immunity. Mutations in this pathway have been linked to several diseases, such as autoimmune diseases, cancer, and infectious diseases. Targeted therapy has been developed to treat these diseases by blocking the activity of the JAK STAT pathway. These include cytokine or receptor antibodies, JAK inhibitors, and STAT inhibitors. Novel agents are currently undergoing testing in preclinical and clinical studies. This article was authored by Chen Shua, Qin Fangyao, Sinyu Jiu, and others.