Adult mesenchymal stem cells (MSCs) are a population of multipotent cells found primarily in the bone marrow. They have long been known to be capable of osteogenic, adipogenic and chondrogenic differentiation and are currently the subject of a number of trials to assess their potential use in the clinic. Recently, the plasticity of these cells has come under close scrutiny as it has been suggested that they may have a differentiation potential beyond the mesenchymal lineage. Myogenic and in particular cardiomyogenic potential has been shown in vitro. MSCs have also been shown to have the ability to form neural cells both in vitro and in vivo, although the molecular mechanisms underlying these apparent transdifferentiation events are yet to be elucidated. We describe here the cellular characteristics and differentiation potential of MSCs, which represent a promising stem cell population for future applications in regenerative medicine.