Mesenchymal stem cells (MSC) are derived from mesodermal precursor and are committed towards mesenchymal differentiation. They are scattered all over the organism, situated in bone, cartilage, adipose tissue and accompany organs for tissue regeneration and structural and functional support. MSC populations are not homogenous, their signature is variable according to their localization. A process called “epithelial mesenchymal transition” is fundamental for the development of mesoderm. Epithelial-mesenchymal interactions specify MSC and this may influence their regeneration potential. Multipotent adult MSC are used for research in tissue regeneration and engineering. Crude mixtures of bone marrow- derived MSC are clinically applied for tissue healing, but complex transplantable tissue engineered constructs are still under development. The role and regeneration potential of MSC in inflammation and ageing organisms remains to be characterized. The establishment of reprogrammed homogenous MSC cultures of high plasticity might allow developing these cells towards multiple cell-based therapeutic strategies. Many applications can be envisioned, e.g. regeneration of bone, cartilage and tendon or engineering of beta cells and neurons. Since homogenous MSC with high plasticity represent a promising tool for the treatment of many diseases, research in this area of adult stem cells should be supported with high priority.