This book offers a state-of-the-art report on recent discoveries concerning the basic and clinical, neuroscientific and psychiatric findings in depression research. Depressive disorder is a severe and recurrent brain disorder that can manifest in depressive mood, somatic symptoms and cognitive impairment. The underlying mechanisms of depressive disorder and its clinical practice are subjects of long-standing interests. This book is a biologically plausible and multilevel theory which describes neural, physiological, molecular and genomic mechanisms that drive depression pathogenesis, as well as navigates the clinical practice and management for depressive disorder. It mainly describes advances made over the past 20 years on the neural, molecular, neuroimaging, physiology, pathophysiology, pharmacology and internet-based measurement and management of depressive disorder. It will help postgraduate students and academic researchers to get either basic or clinical picture of depressive disorder. Also, it may benefit pharmaceutical companies for developing novel drugs to treat this disease.