For many years, it has long been known that stem cells derived from adult tissues maintain the capacity for self-renewal and differentiation into multiple cell types that are characteristic of the tissue of origin. Recent studies have shown new evidence that several tissues may contain cells capable of generating differentiated cells beyond their own tissue boundaries, defining a process termed stem cell plasticity. The pluripotency of adult stem cells have evoked significant excitement over the possibility of novel functional uses of stem cells, with the final purpose to develop new and more effective treatment strategies. However, despite the number of promising studies describing the plasticity of adult stem cells, many questions remain to be answered. In this article, we critically review the current state of the art in the field of adult stem cells, focussing on the present understanding of the concepts of stem cell pluripotency and plasticity.