Abstract Mitochondrial dysfunction is associated with numerous diseases, including disorders of thrombosis and hemostasis. Platelets inherit fully functional mitochondria from megakaryocytes, yet how megakaryocytes maintain mitochondrial integrity and function during their unique developmental process is unknown. Genetic studies have associated the mitochondrial maintenance and fusion protein Mitofusin 2 (MFN2) with platelet counts and cardiovascular disease. Our preliminary data show that loss of MFN2 in human platelets is associated with accelerated platelet death in vitro. Knockout of MNF2 in mice reduced platelet survival, and impaired hemostasis and thrombosis. Preliminary data suggest a mitochondrial role: loss of MFN2 disrupted mitochondrial morphology in megakaryocytes, and impaired mitochondrial function in platelets. In Aim 1 we test the hypothesis that MFN2 maintains mitochondrial integrity and function during megakaryocyte development to ensure platelets inherit fully functional and long-lived mitochondria. In Aim 2 we test the hypothesis that loss of MFN2 leads to platelet death, dysfunction, and altered hemostasis and thrombosis. Because MFN2 is especially important in adapting to metabolic stress, we will test each of these hypotheses under normal conditions and during metabolic stress. Each aim will have a mouse and human component: for mouse studies we will use platelet/megakaryocyte specific MFN2 knockouts, and for human studies we will utilize primary cells harboring a genetic variant that significantly reduces MFN2 expression in platelets. This work is significant because the results may lead to new approaches to target disorders of thrombosis and hemostasis, and improve platelet production and storage. This work is innovative: we will examine mitochondrial fusion, a novel pathway regulating platelet survival and function in health, during metabolic stress, and in transfused platelets. We will use innovative methods to examine mitochondrial function in new and circulatory aged platelets. Our studies will provide new insights into how MFN2 affects platelet death and dysfunction, an important step into understanding why human MFN2 variants are associated with platelet counts and cardiovascular disease.