Mesenchymal stem cells (MSCs) are adult stem cells able to give rise to mature mesenchymal cell types. Plastic-adherent cells are operationally defined as MSCs based on their ability to proliferate and differentiate into cells such as osteoblasts, adipocytes and chondrocytes. In the past ten years, cultured MSCs have been shown to exhibit great plasticity in culture, as they can differentiate into cells with ectodermal and endodermal characteristics, suggesting their use as a source of cells to treat different diseases. More recently, cultured MSCs were found to secrete various bioactive molecules that display anti-apoptotic, immunomodulatory, angiogenic, anti-scarring, and chemoattractant properties, providing a basis for their use as tools to create local regenerative environments in vivo. Whereas the properties of cultured MSCs have been studied for a long time, their exact location in vivo is slowly becoming apparent as evidence indicates that pericytes behave as stem cells throughout the organism. In this review, we discuss some aspects of MSC basic biology, the methodology involved in MSC culture, and some clinical and pre-clinical applications of cultured MSCs.