Recent years have seen great strides in research on the pathogenesis of thromboses, unmatched by progress in other branches of hemostasiology. The orthodox concepts of the mechanisms of thrombus formation described by Virchow have come down to us as a "classical triad" of factors. Now, due to developments in molecular biology, pharmacology, and patho­ physiology, they appear in a basically new light. The fruits of modern research, currently being tested or already imple­ mented in clinical practice, have opened up the possibility of controlling the hemostatic process and developing effec­ tive antithrombotic drugs. Much progress has been achieved in the past years, but much more remains to be achieved in such areas as the patho­ genesis of venous and arterial thromboses, early diagnosis, therapy, and control of disorders. Many scientists in the U.S.S.R. are involved in studying these problems. Their data, from years of research carried out in leading laboratories and clinics in the U.S.S.R., are summarized in this monograph. This work is written by experts in various fields of biology and medicine. It deals with new and original con­ cepts on the structure and function of the fibrinolytic sys­ tem, the role of nonenzymatic fibrinolysis in regulating physiological hemostasis, the heterogeneous and discrete pat­ terns of the system regulating blood coagulation, the molecu­ lar mechanisms of fibrin polymerization, and the anticoagu­ lating effects of fibrinogen/fibrin degradation products.