This volume highlights the remarkable new developments in brain imaging, including those that apply magnetic resonance imaging (MRI) and Positron Emission Tomography (PET), that allow us to non invasively study the living human brain in health and in disease.  These technological advances have allowed us to obtain new and powerful insights into the structure and function of the healthy brain as it develops across the life cycle, as well as the molecular make up of brain systems and circuits as they develop and change with age.  New brain imaging technologies have also given us new insights into the causes of many common brain disorders, including ADHD, schizophrenia, depression and Alzheimer's disease, which collectively affect a large segment of the population.  These new insights have major implications for understanding and treating these brain disorders, and are providing clinicians with the first ever set of biomarkers that can be used to guide diagnosis and monitor treatment effects. The advances in brain imaging over the last 20 years, summarized in this volume, represent a major advance in modern biomedical sciences.   The Authors of this volume are leaders in the development of PET and MRI methods as well as clinical and translational researchers skilled in their use in patients with brain disorders. Individual chapters of this volume focus on the use of specific methodologies, covering the full range of PET chemistry based approaches as well as MRI methods from structural and diffusion tensor based imaging, to functional MRI of functional brain circuitry, to pharmacological MRI and MRI spectroscopic molecular imaging. .