This document summarizes the cells involved in the innate and adaptive immune system. The innate immune system contains myeloid cells like neutrophils, eosinophils, basophils, mast cells, monocytes, macrophages, and dendritic cells that provide non-specific first line defense against pathogens. The adaptive immune system contains lymphocytes like T cells and B cells that provide specialized and targeted defense. T cells regulate the immune response and destroy intracellular pathogens. B cells produce antibodies for specific antigens encountered.