The main objective of this book is to present a thorough update on stem cell research and the potential therapeutic applications of stem cells. The text is structured following a path that starts from the molecular basics and the biological properties of pluripotent, embryonic, or reprogrammed stem cells, and it compares the different degrees of stemness while describing the adult stem populations residing in the various tissues and organs of the human body and finally introduces the most recently discovered perinatal stem cells, derived from placental tissues. Starting from basic research, the book discusses examples of regenerative medicine that translate the experimental findings into clinical applications of cell therapy. Finally, the book reviews how stem cells represent a model for understanding the physiological mechanisms that control their fate, and the pathological mechanisms involved in the aberrant biology of cancer stem cells. Each chapter has been conceived by distinguished researchers who provide detailed and updated contributions that distill knowledge in a very readable text.