Cell identity is a fundamental feature of cells. Tissues are often organized into cellular hierarchies characterized by progressive differentiation and developmental commitment. However, it is been historically evident that the cells of many organisms of various phyla, especially in the context of injury, exhibit remarkable plasticity in terms of their ability to convert into other cell types. Recent modern studies, using genetic lineage tracing, have demonstrated that many mature functional cells retain a potential to undergo lineage reversion (dedifferentiation) or to convert into cells of other more distant lineages (transdifferentiation) following injury. Similarly, mimicking progenitor cell transdetermination, stem cells can interconvert. These forms of plasticity may be essential for organismal survival, and are likely part and parcel of regeneration.