This book summarizes the latest findings about the role of cancer stem cells (CSCs) in cancer biology and how this knowledge could be used for novel anticancer therapies. It provides an overview of CSCs in selected malignancies with particular emphasis on hematopoietic neoplasias. It then reviews the role of CSCs in metastasis formation and initiation of cancer relapses. It also examines the dark site of cancer therapy such as conventional cancer therapies that may lead to the origin of recurrence CSCs. Finally, it supplies a brief overview of current concepts that may allow for a selective eradication of CSCs.