The concept of mesenchymal stem cells has gained wide popularity. Despite the rapid
growth of the field, uncertainties remain with respect to the defining characteristics of these
cells, including their potency and self-renewal. These uncertainties are reflected in a
growing tendency to question the very use of the term. This commentary revisits the
experimental origin of the concept of the population (s) referred to as mesenchymal stem
cells and the experimental framework required to assess their stemness and function.