The Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway is a critical signaling pathway that transmits extracellular signals to the nucleus, playing essential roles in various physiological functions such as hematopoiesis, immune balance, tissue homeostasis, and tumor surveillance. Dysregulation of this pathway can lead to diseases including immune deficiencies, autoimmune disorders, hematologic disorders, and cancer. Extensive research has been conducted on the JAK-STAT pathway, ranging from basic science to medical applications. Advances in structural biology, particularly cryo-electron microscopy (cryo-EM), have provided insights into the molecular mechanisms of the pathway, enabling the development of targeted therapies. Small molecule inhibitors, such as ruxolitinib and tofacitinib, have shown promise in treating autoimmune and hematopoietic diseases. Additionally, cytokine engineering has led to the development of cytokines with tailored properties for therapeutic applications. The JAK-STAT pathway's involvement in various diseases has made it an attractive target for drug development, with over 10 small molecules currently approved for clinical use and many more in development. The pathway's role in inflammation and cancer has also led to its exploration as a therapeutic target, with cytokine inhibitors showing efficacy in managing hyperinflammatory conditions like cytokine storms. The review covers the structural basis of key nodes in the JAK-STAT pathway, the therapeutic potential of cytokine engineering, and the role of the pathway in various diseases.The Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway is a critical signaling pathway that transmits extracellular signals to the nucleus, playing essential roles in various physiological functions such as hematopoiesis, immune balance, tissue homeostasis, and tumor surveillance. Dysregulation of this pathway can lead to diseases including immune deficiencies, autoimmune disorders, hematologic disorders, and cancer. Extensive research has been conducted on the JAK-STAT pathway, ranging from basic science to medical applications. Advances in structural biology, particularly cryo-electron microscopy (cryo-EM), have provided insights into the molecular mechanisms of the pathway, enabling the development of targeted therapies. Small molecule inhibitors, such as ruxolitinib and tofacitinib, have shown promise in treating autoimmune and hematopoietic diseases. Additionally, cytokine engineering has led to the development of cytokines with tailored properties for therapeutic applications. The JAK-STAT pathway's involvement in various diseases has made it an attractive target for drug development, with over 10 small molecules currently approved for clinical use and many more in development. The pathway's role in inflammation and cancer has also led to its exploration as a therapeutic target, with cytokine inhibitors showing efficacy in managing hyperinflammatory conditions like cytokine storms. The review covers the structural basis of key nodes in the JAK-STAT pathway, the therapeutic potential of cytokine engineering, and the role of the pathway in various diseases.