The reference book contains modern aspects of theoretical and clinical hematology, the most recent data on hematopoiesis, morphology and functions of blood cells and bone marrow, hematopoietic microenvironment, as well as information on cytogenetics, immunohematology, immunohistochemistry and the hemostasis system. Modern methods of diagnosing and treating diseases of the blood system are presented, issues of their etiopathogenesis are considered.