There are two ways that we can obtain stem cells, one are embryonic stem cells (ESCs) and the other are adult-derived stem cells (ASCs), the latter are less pluripotent though. It is also possible to get embryonic germ cells (EGCs), which are the ancestors of sperm and egg cells, but I don't see how it is morally any different to use these instead of ESCs. But why can't we just make them in culture? What is it that makes a stem cell totipotent and how much does imprinting play a role in this? For those who don't know, stem cells have the ability to differentiate in any kind of tissue, thus opening the door to tissue (or even organ) regeneration.