Embryonic Stem Cells (ESCs) are pluripotent cells derived from the inner cell mass of blastocysts. These cells are able to differentiate into all derivatives of the primary germ layers, including ectoderm, endoderm, and mesoderm, thus generating every cell type in the body. Different from most other stem cells, ESCs are capable of self-renewal indefinitely. Because of their plasticity and potentially unlimited capacity for self-renewal, ES cell therapies have been proposed for regenerative medicine and tissue replacement.