The cloning of thrombopoietin together with advances in the culture of hematopoietic stem cells have paved the way for the study of megakaryopoiesis, ongoing clinical trials and, in the future, for the potential therapeutic use of ex vivo produced blood substitutes, such as platelets. This chapter describes a 14-day culture protocol for the production of human megakaryocytes (MKs) and platelets, and assays that can be used to characterize the functional properties of the platelets produced ex vivo. CD34+ cells isolated from cord blood cells are grown in a serum-free medium supplemented with newly developed cytokine cocktails optimized for MK differentiation, expansion, and maturation. Detailed methodologies for flow cytometry analysis of MKs and platelets, for the purification of platelets and functional assays, are presented together with supporting figures. The chapter also provides a brief review on megakaryocytic differentiation and ex vivo MK cultures.