While the potential of stem cells is recognized, their proliferation and differentiation must be more precisely controlled to maximize the production of therapeutically relevant cells and for cell replacement therapies to minimize contamination with residual cells that can give rise to side effects. With contributions from pioneers and experts, this book provides a broad overview of the challenges of stem cell engineering. It discusses advances made during the last decade that have led to increasingly defined culture systems for growing human ES cells, starting from co-culture with feeder cells in the presence of serum to growth on synthetic substrates in defined medium. The book highlights recent advances in the understanding of the cellular and molecular composition of the hematopoietic stem cell niche, as well as approaches to build upon this basic information to direct stem cell differentiation into blood cell lineages.