White blood cells (WBCs, leukocytes) are nucleated cells produced from bone marrow; they have a role in body immunity. They form the first line of defense of the body against invading microorganisms. White blood cells are classified either as polymorphonuclear leucocytes (or granulocytes) or as mononuclear cells. Granulocytes are further divided into three subtypes, Neutrophils, eosinophils, and basophils. Mononuclear cells indicate both lymphocytes and monocytes. The Book reviews the production, morphology, distribution and kinetics, functions, non-neoplastic disorders, and inherited and acquired abnormalities of the white blood cells. An attempt is made to provide the reader with a working knowledge of the white blood cells in contemporary hematology. This book is designed to generate an overall knowledge with the WBCs for hematologists, practitioners, educators and students to accomplish an excellent overview of the topic.