Human normal immunoglobulin (IVIG) is indicated for immune replacement therapy in primary and secondary immunodeficiency, as well as for immunomodulation in autoimmune and inflammatory diseases such as Guillain–Barré syndrome, immune thrombocytopenia, Kawasaki disease, and severe infections. Its key advantage is a dual mechanism: it provides immediate passive immunity by supplying functional antibodies, while also modulating the immune response to reduce pathological inflammation. In hospital and ICU settings, IVIG is particularly valuable when rapid immune support is required or when conventional therapies are insufficient. It helps neutralize pathogens, regulate cytokine activity, and improve clinical outcomes in critically ill patients. Its broad applicability, rapid onset, and well-established safety profile make IVIG an essential therapy in modern clinical practice.