The GRC Meeting on the Cell Biology of Megakaryocytes and Platelets will focus on the transcription and growth factors that influence hematopoietic stem cell expansion and differentiation into progenitor cells committed to the megakaryocyte lineage, the cellular and molecular mechanisms by which these cells undergo a series of remarkable and unique biological processes, including endomitosis and proplatelet formation, and how megakaryocytes and platelets receive and send signals that contribute to their roles in hemostasis, thrombosis and metastatic cancer. Three sessions will focus on the generation of megakaryocytes in health and disease, specifically how the genes that determine this lineage are activated, the molecular events that occur during endomitosis and platelet biogenesis, and how disorders of these processes result in congenital and acquired disorders of platelet number and function. Three sessions are also devoted to the signals that transmit the vascular clues resulting in platelet activation, and how those internal signals enhance platelet reactivity, outside-in and inside-out signaling. Finally, three sessions are devoted to understanding the mechanisms that account for the role of platelets and their progenitors in vascular pathology, myeloproliferative diseases and supporting the metastatic spread of cancer.