All mature blood cells are derived from hematopoietic progenitors that have been defined by their ability to generate colonies of cells in semisolid media. Investigation of the cellular components of these colonies has confirmed the existence of unilineage, bilineage, and multilineage progenitors. Furthermore, it has led to a better understanding of the relationships that exist among the erythroid, myeloid, and megakaryocyte lineages that compose much of the hematopoietic hierarchy in the adult. More recently, the development of hematopoietic progenitors has been investigated in the mammalian embryo. The first progenitors arise in the yolk sac and subsequently expand in the fetal liver before settling into the postnatal bone marrow. This chapter describes the methodologies for the culture and identification of unipotential and multipotential hematopoietic progenitors in the mouse embryo.