The initial isolation of ES cell lines in 1981 was a major breakthrough for developmental biology as it provided a simple model system to study the basic processes of early embryonic development and cellular differentiation.

Embryotic stem cells derived from human blastocysts have the capacity for multilineage differentiation and can be used for cell-based therapies in which virtually any tissue or cell type could be produced ‘to order’ in the laboratory. This would provide a radical new approach to the treatment of a wide variety of diseases where organ damage or dysfunction exceeds the body's capability for natural repair. The derivation of human ES cells finally made regenerative medicine and tissue engineering a real possibility for the future treatment of human disease. Also, the potential of ES cells in transplantation medicine is vast.

Embryonic stem cells have huge potential in the field of tissue engineering and regenerative medicine as they hold the capacity to produce every type of cell and tissue in the body. These cells could be expanded continuously in culture and could also be induced to differentiate into derivatives of all three embryonic germ layers; endoderm, ectoderm and mesoderm. The treatment of human disease could be revolutionized by the ability to generate any cell, tissue, or even organ, ‘on demand’ in the laboratory.

Embryotic stem cells, unlike any other stem cell, can be used for cloning. The cloning of humans is extremely controversial. However, many mammal embryos have been cloned, including a primate embryo, and in theory, a human embryo could be cloned.