Embryonic stem cells (ES cells) are stem cells derived from the inner cell mass of an early stage embryo known as a blastocyst. Human embryos reach the blastocyst stage 4-5 days post fertilization, at which time they consist of 50-150 cells. Embryonic Stem (ES) cells are pluripotent. This means they are able to differentiate into all derivatives of the three primary germ layers: ectoderm, endoderm, and mesoderm.

Simply defining, embryonic stem cells are stem cells derived from the inner cell mass of an early stage embryo known as a blastocyst. Human embryos reach the blastocyst stage 4-5 days post fertilization, at which time they consist of 50-150 cells. Embryonic stem cells are pluripotent, which means that they have the ability to differentiate into organized masses of tissues or organs.

The results of this experiment suggested an improvement in locomotor recovery in spinal cord-injured rats after a 7-day delayed transplantation of human ES cells that were pushed towards an oligodendrocytic lineage.

One of the greatest advantages of embryonic stem cell research is the possibilities associated to cloning. Embryonic stem cells are the ideal candidates for cloning. They contain information on every cell in the body and they can be manipulated in nearly any way imaginable. Scientists believe they can grow limbs and organs that could be transplanted into humans. These could be exact DNA matches which would make the transplant process more efficient and have a greater chance of succeeding.

Embryonic stem cells (ES cells) were first derived from mouse embryos in 1981 by Martin Evans and Matthew Kaufman and independently by Gail R. Martin. Gail R. Martin is credited with coining the term 'Embryonic Stem Cell'. A breakthrough in human embryonic stem cell research came in November 1998 when a group led by James Thomson at the University of Wisconsin-Madison first developed a technique to isolate and grow the cells when derived from human blastocysts.

Embryonic stem cell research has been promoted because it has the ability to cure a number of deadly diseases.