The multipotential progenitor cells called ,Mesenchymal Stem Cells" (MSC) are capable of differrentiation at least into bone, cartilage, and adipose tissues. The commonly recognized role of these cells is the formation of connective tissue which participates in formation of every organ. The progeny of MSC produces also the hematopoietic microenvironment, recently it have been documented that these cells are capable of the modulation of the immune system activities. MSC are isolated from the tissues of fetal origin (umbilical cord, cord blood, or placenta), or from several adult donor sites, in particular from bone marrow and adipose tissue which are most useful for practical purposes. The capability of multipotential differentiation, immunomodulation, and the regulation of the endogenous tissue repair are the reasons why mesenchymal stem cells are widely applied for regenerative medicine purposes.