Embryonic stem (ES) cells are pluripotent cells derived from blastocyst-stage embryos. They are characterized by their infinite self-renewal capacity and their ability to differentiate into many cell types in vitro as well as in vivo. The present protocol describes culture conditions that allow efficient differentiation of mouse ES cells toward the endothelial lineage, both in two-dimensional cultures and in three-dimensional, multicellular embryoid bodies. We also provide a protocol for establishing recombinant ES cell clones, giving the example of cells expressing green fluorescent protein and an antibiotic resistance gene under the control of an endothelial-specific promoter. These transgenes allow the visualization and the genetic selection of endothelial cells from a heterogeneous population of differentiating ES cells. Potential applications for these differentiation models are given, including the study of the endothelial cell lineage and its derivatives, the testing of molecules involved in angiogenesis, and the potential use of selected endothelial cells in vivo.