The formation of a hemostatic plug to staunch blood loss at sites of vascular injury relies on the dynamical processes of activation of the coagulation cascade and platelet recruitment in the setting of the biorheology of blood flow. Thus, elucidation of the molecular mechanisms of thrombus formation ex vivo relies on the use of biomedical engineering principles to design platforms to study complex enzymatic reactions and cell biology under physiologically relevant shear flow conditions. The focus of this dissertation work is the development and testing of microfluidic platforms to study blood reaction dynamics in health and disease. The ultimate goal of this work is to expand our understanding of the (patho)physiology of thrombosis and hemostasis and determine how can we intervene with one without compromising the other.