Research on stem cells can confuse a person not familiar with the field. What is an embryonic stem cell? What is an adult stem cell? What is a pluripotent cell compared to a unipotent one? How does each one work in normal development or cause cancer when things go wrong? And what is the potential for manipulating them to treat disease? In this lecture, Luis Parada, Ph.D., will review the science of stem cells and how current animal models provide biological information that is applicable to human biology and disease.