The dentate gyrus is a part of the brain that has been a topic of intense interest since the beginning of neuroscience, and pioneering studies from the distant and recent past attest to this. One of the reasons for such interest is that this structure provides some of the most remarkable examples of plasticity within the nervous system. In addition, it is critical to normal cognitive function, although exactly how and when is still a question that eludes answers. Furthermore, abnormalities within the dentate gyrus appear to play a role in diverse clinical conditions, from depression to epilepsy and traumatic brain injury. The primary goal of this book is to provide a context, or background, upon which the detailed knowledge of the current era can be appreciated. A series of overviews are provided to clarify essentials related to structural organization and development, cellular components, neurotransmitters and neuromodulators, plasticity, and clinical relevance.