Instructing glial cells to generate neurons may prove a strategy to replace neurons that have degenerated. Here we describe a robust protocol for the efficient in vitro conversion of postnatal astroglia from the murine cerebral cortex into functional, synapse-forming neurons. This protocol involves two steps: (i) expansion of astroglial cells (7 days) and (ii) astroglia-to-neuron conversion induced by persistent and strong retroviral expression of Neurogenin2 or Mash1 and/or Dlx2 for generation of glutamatergic or GABAergic neurons, respectively (7-21 days for different degrees of maturity). Our protocol of astroglia-to-neuron conversion by a single neurogenic transcription factor provides a stringent experimental system to study the specification of a selective neuronal subtype, thus offering an alternative to the use of embryonic or neural stem cells. Moreover it can be a useful model for studies of lineage conversion from non-neuronal cells with potential for brain regenerative medicine.