Human stem cell research came to the fore in the late 1990s. It is generally divided into embryonic and adult (postnatal sources). In the earliest days of human development, the cells of the newly developing life have the potential to become the different cells of the developed human body. These early embryonic cells are called pluripotent. The developed human body has basic cells that produce specific kinds of cells for the continuation of the body's life. Scientists are experimenting with how they can use these embryonic and adult stem cells to heal the body.

Adult stem cells present no basic moral problem and, unlike embryonic stem cells (which are difficult to use), are already in trials producing therapeutic benefits to patients. However, the process of harvesting embryonic stem cells from a living human embryo results in the embryo's death and is thus fundamentally immoral.

Some scientists are attempting to derive embryonic stem cells from cloned human embryos. This is sometimes called "therapeutic cloning," though the cloning process is the same whether the cloned embryo is killed for research - not at all therapeutic for the embryo - or is allowed to come to birth. Some want to use government funds to support this kind of research.

In 1996 Congress passed the Dickey-Wicker Amendment banning federal funding of research harmful to the human embryo. In 1999, the Clinton Administration interpreted the Dickey-Wicker Amendment to mean that federal funds could not be used to derive stem cells from the embryo, but could be used for research on the cells after they had been derived. On August 9, 2001, President Bush announced that federal funding would be available only for research on human embryonic stem cell lines already in existence as of that date.

In 2007, studies were published showing how induced pluripotent stem cells (iPS cells) can be produced by direct reprogramming of adult cells. The iPS cells have the properties of human embryonic stem cells but are generated without destroying human embryos. A growing number of scientists think that the iPS cells breakthrough will make embryonic stem cell research a thing of the past.

On March 9, 2009, President Barack Obama issued an Executive Order overturning the Bush Administration embryonic stem cell research policy. On July 7, 2009, the National Institutes of Health (NIH) published final guidelines implementing the Obama directive, opening the door for the use of federal taxpayer dollars for research on human embryonic stem cells that are derived by killing human embryos acquired from fertility clinics.

Subsequently, on August 23, 2010, Royce C. Lamberth, Chief Judge of the U.S. District Court for the District of Columbia, issued a preliminary injunction that enjoined the government from implementing the guidelines on the grounds they violate the Dickey-Wicker Amendment. Legislation has been introduced that would overturn the Dickey-Wicker Amendment and authorize a broad range of embryonic stem cell related research funding.

Also see: Umbilical Cord Blood Banks.