Furin is a versatile endoprotease that plays a crucial role in the maturation of proprotein substrates in the secretory pathway. Its broad and diverse functions extend beyond this basic biochemical role, impacting homeostasis and various diseases. This review covers the structural and enzymatic properties of furin, its intracellular localization and trafficking, substrate specificity, and its roles in vivo. Furin is essential for embryogenesis and the maturation of a wide range of proprotein substrates, including growth factors, receptors, extracellular matrix proteins, and other protease systems. It is also involved in the activation of pathogenic agents such as bacterial toxins and viral envelope glycoproteins. The review highlights the importance of furin in determining the pathogenicity of viruses and bacteria, and discusses its potential as a therapeutic target in diseases like cancer, dementia, and viral infections.Furin is a versatile endoprotease that plays a crucial role in the maturation of proprotein substrates in the secretory pathway. Its broad and diverse functions extend beyond this basic biochemical role, impacting homeostasis and various diseases. This review covers the structural and enzymatic properties of furin, its intracellular localization and trafficking, substrate specificity, and its roles in vivo. Furin is essential for embryogenesis and the maturation of a wide range of proprotein substrates, including growth factors, receptors, extracellular matrix proteins, and other protease systems. It is also involved in the activation of pathogenic agents such as bacterial toxins and viral envelope glycoproteins. The review highlights the importance of furin in determining the pathogenicity of viruses and bacteria, and discusses its potential as a therapeutic target in diseases like cancer, dementia, and viral infections.