Neurogenesis is the process by which nervous system cells, the neurons, are produced by neural stem cells (NSCs). It occurs in all species of animals except the porifera (sponges) and placozoans. Types of NSCs include neuroepithelial cells (NECs), radial glial cells (RGCs), basal progenitors (BPs), intermediate neuronal precursors (INPs), subventricular zone astrocytes, and subgranular zone radial astrocytes, among others. Neurogenesis is most active during embryonic development and is responsible for producing all the various types of neurons of the organism, but it continues throughout adult life in a variety of organisms. Once born, neurons do not divide (see mitosis), and many will live the lifespan of the animal.

During embryonic development, the mammalian central nervous system (CNS; brain and spinal cord) is derived from the neural tube, which contains NSCs that will later generate neurons. However, neurogenesis doesn't begin until a sufficient population of NSCs has been achieved. These early stem cells are called neuroepithelial cells (NEC)s, but soon take on a highly elongated radial morphology and are then known as radial glial cells (RGC)s.

Neurogenesis can be a complex process in some mammals. In rodents for example, neurons in the central nervous system arise from three types of neural stem and progenitor cells: neuroepithelial cells, radial glial cells and basal progenitors, which go through three main divisions: symmetric proliferative division; asymmetric neurogenic division; and symmetric neurogenic division.