The birth of new neurons in the adult mammalian brain-once thought impossible-is now a well-accepted phenomenon that takes place in the subventricular zone of the lateral ventricles and the hippocampus. This review focuses on the recent work that has sharpened our views of how hippocampal newborn neurons are regulated and function. Areas of study include (a) how neurogenesis contributes to behavioral pattern separation, (b) how pattern separation may be influenced by the properties and circuitry of newborn neurons, (c) differences along the dorsal-ventral axis of how neurogenesis is regulated and functions, and (d) adult neurogenesis in primates, including new human data. These current avenues of research reveal new details of adult neurogenesis and foreshadow what we may learn about this exciting phenomenon in the near future.