Cellular conversion is a process of genetic reprogramming by various methods to induce the direct transformation of one type of cell into another without going through other intermediate states. Neuronal loss is a common pathological process in a variety of neurological disorders, including Parkinson’s disease, Alzheimer’s disease, and stroke. Neuronal loss is usually irreversible and causes motor, sensory, and psychiatric symptoms. Since the human central nervous system has limited capacity for neuronal regeneration, therapeutic strategies that use glial cells (astrocytes, microglia, and oligodendrocyte precursor cells) to transdifferentiate into functional neurons in situ of neuronal loss and integrate them into neural networks have received much attention. In recent years, successful conversion of glia-to-neuron by manipulating the gene expression of key transcription factors in neuronal fate determination in glial cells has been discovered. Nevertheless, there is still some controversy about the scientific validity of some research technologies, the rationality of judgment criteria, and the self-consistency between experimental results and conclusions. This article reviews the discovery and development of glia-to-neuron conversion and takes astrocytes, microglia, and oligodendrocyte progenitor cells as examples to summarize the important findings of glia-to-neuron conversion with discussion and perspective.