Stem-cell research is en vogue — 25 years after scientists first isolated mouse embryonic stem cells, it is now possible to isolate and culture stem cells from embryos and adult tissues of many species, including humans. Despite the rapid progress in this field, several important questions in the areas of embryonic and adult stem-cell research still remain unanswered. What are the cellular and molecular mechanisms that underlie stem-cell renewal while conveying the potential to differentiate to different cell lineages? What combination of molecules confers differentiation to specific cell types? How can we isolate stem cells from different tissues? And how will knowledge of the mechanisms that underlie self-renewal and differentiation help us to develop patient-specific therapies?

In a Series of specially commissioned articles, Nature Reviews Molecular Cell Biology reports on the current hot and exciting topics in stem-cell research, discusses new technologies and resources to study stem cells and explores controversial issues, such as stem-cell ethics and funding.