"Inside an embryo no bigger than the period at the end of this sentence are dozens of stem cells. Initially, these cells are blank slates, meaning that their fate is undecided. But they have great potential. Stem cells are pluripotent, which means that they can develop into every cell, every tissue and every organ in the human body.
Their almost limitless potential has made stem cells a significant focus of medical research. Imagine having the ability to return memory to an Alzheimer's patient, replace skin that was lost during a terrible accident or enable a wheelchair-bound person to walk again.
But before scientists can use stem cells for medical purposes, they must first learn how to harness their power. They can't treat disease until they learn how to manipulate stem cells to get them to develop into specific tissues or organs."
This article explains stem cell basics and is an excellent primer to allow you to better understand the fierce debate surrounding their research and use.