Embryonic stem (ES) cells are pluripotent cells derived from the inner cell mass cells of blastocystwith the potential to maintain an undifferentiated state indefinitely. Fully characterized ES cell linesexpress typical stem cell markers, possess high levels of telomerase activity, show normal karyotypeand have the potential to differentiate into numerous cell types under in vitro and in vivo conditions.Therefore, ES cells are potentially valuable for the development of cell transplantation therapies for thetreatment of various diseases in animals as well as in humans. However, important problemsassociated with ES cells from in vitro fertilized blastocysts particularly from humans must be resolvedbefore taking up its therapeutic applications. Current techniques for directed differentiation intosomatic cell populations remain inefficient and yield heterogeneous cell populations. This reviewtherefore focuses on ES cells with respect to in vitro propagation and differentiation in basic cell anddevelopmental biology for successful use of these cells in therapeutics.