The 21st century is considered as the era of Biotechnology (BT). Recently, the regenerative medicine using stem cells has been recognized as the future medicine, especially for the devastating diseases such as neurodegenerative diseases, heart disease, diabetes, infertility and liver diseases. Human embryonic stem cells (hESCs) are at the center of the stem cell research due to its ability to proliferate unlimitedly without differentiation (self-renewal) and to differentiate into the derivatives of all three germ layers including germ cells with appropriate treatments (pluripotency). A total of 173 hESC lines have been derived since the first derivation by Thomson et al. in 1998, and 70 hESC lines are currently available for distribution including hESC line (Miz-hES1) established at the MizMedi Hospital. The major goal of hESC research is to provide basic and clinical clues for cell replacement therapy, whose targets are aforementioned incurable diseases. One of the landmarks in hESC research is the derivation of a hESC line from a cloned human blastocyst, which has recently been done by Korean scientists. This made it possible to overcome the issue of immune-mediated rejection following cell replacement therapy using hESCs. Guided differentiation of hESCs into specific cell types by treating growth factors and drugs or by genetic manipulation by using overexpression or an RNAi knockdown system is one of the most active research areas. Combined efforts towards the guided differentiation of hESC into specific cell types and the cloning of hESC from a cloned human blastocyst will overcome a list of diseases hitherto considered to be incurable.