The discovery of adult neurogenesis and of stem cells in the adult brain has changed our view of the mature brain. With new neurons being produced lifelong, brain development does not seem to end and brain plasticity gains a whole different meaning, if the brain's malleability goes beyond synapses and neurites. But adult neurogenesis occurs in two privileged regions only, the hippocampus and the olfactory system. Since the mid-1990s, the field of adult neurogenesis research has literally exploded. The second edition became necessary, after hundreds of new reports had been published. Most progress has been made with respect to the question of the functional relevance of the new neurons and their contribution to learning and memory. The book has become a reference resource for everybody interested in adult neurogenesis and stem cell biology of the adult brain. It begins with the historical background and describes in detail adult neurogenesis in the hippocampus as well as the subventricular zone and olfactory bulb. Regulatory mechanisms are discussed in great detail. The subject of neurogenesis outside the "canonical" neurogenic regions of rodents and primates is discussed and an entire chapter is dedicated to adult neurogenesis in different species. The book concludes with a chapter on the provocative hypotheses that link failing adult neurogenesis with diseases such as temporal lobe epilepsy, major depression, schizophrenia, brain tumors, and dementias.