Stem cells are the body's master cells and have the ability to produce all manner of tissues. Embryonic stem(ES) cells, derived from the inner cell mass(ICM) of the mammalian blastocyst, can continuously proliferate in an undifferentiated state and differentiate into a desired cell lineage under certain conditions. These abilities make ES cells an appealing source for cell replacement therapies, the study of developmental biology, and drug/ toxin screening studies. Compared to mouse ES cells, human ES cells have only recently been derived and studied. Although there are many differences in properties between mouse and human ES cells, the study of mouse ES cells has provided important insight into human ES cell research. In this review, I describe the advantages and disadvantages of methods used for human ES cell derivation, the expansion of human ES cells.