This presentation provides a comprehensive overview of the human immune system, detailing its primary roles in defense, homeostasis, and surveillance. It categorizes immunity into innate and acquired types, while identifying the central and peripheral lymphoid organs, such as the bone marrow and spleen, that facilitate these biological processes. The material highlights essential cellular players, including mast cells and various white blood cells measured in a standard blood count. Special attention is given to the immune response, distinguishing between humoral immunity involving antibodies and cell-mediated immunity driven by T-cells. Finally, the document illustrates the five classes of immunoglobulins and their specific duties in neutralizing pathogens to maintain bodily health.