A complex network of hemostasis proteins maintains the blood flow and integrity of the vascular system. Molecular biology techniques have led to identification and cloning of the corresponding genes, thereby providing the basis for development of various recombinant clotting factor concentrates. Further analysis of these genes allowed for phenotype and genotype correlations in patients with hemorrhagic or thromboembolic disorders and analysis of structure and function relationships of the involved proteins. All these efforts result in a greatly advanced understanding of the hemostatic network. The aim of this article is to illustrate this progress by reporting on the recent results in representative hereditary hemorrhagic and such thromboembolic conditions as hemophilia, von Willebrand disease, and thrombotic disorders.