The various chapters of Stem Cells and Disease describe the role of cancer stem cells and progenitor cells in disease progression and treatment. These reviews cover the gamut of tissue types and cell lines as well as differentiate between normal and diseased cells and tissues. By examining the role of these self-renewing cells in disease it is hoped that the development of novel therapeutics for a variety of afflictions in today’s society can be achieved. It is first necessary to distinguish between embryonic stem cells and adult stem cells. Embryonic stem cells are undifferentiated cells with the ability to undergo asymmetric cell division to form a committed progenitor cell and another self-renewable stem cell. Adult stem cells are those that are either de-differentiated or activated at later stage and are able to self renew and are usually a committed tissue type. Use of adult stem cells holds incredible potential because not only is it possible to study the proliferative aspects of already differentiated tissues, but the application of the knowledge obtained to ‘turn-off’ proliferating cancer cells can possibly be achieved as well. This would be of tremendous benefit for use in therapeutics and treatments of disease. Contributors to this volume have attempted to provide an overview of the developing concepts and controversies in the area of stem cell biology as it relates to disease formation in a variety of tissue types.