This book focuses on risk factors, clinical and biological characteristics, and treatment options for depression. The aim of this book is to provide readers with an up-to-date understanding of the clinical and neurobiological underpinnings of depression as well as promising treatment for depression. The book is divided into five sections, the first of which examines the clinical heterogeneity of depression. Clinical symptoms, risk factors and treatment options of depression during neurodevelopment and neurodegeneration periods differ from those of depression in adults. Section II highlights bio-psychosocial factors in depression. Major depression cannot be understood without considering the psychosocial environment. Interaction between genetic susceptibility and the psychosocial context affect the occurrence of major depression. Section III focuses on biomarkers of depression. It covers from the overview of biomarkers, focusing on diagnosis, subtyping of depression and treatment response prediction to neuroimaging, genetics, and serum markers in depression. Section IV covers neurobiology and management for treatment-resistant depression. It discusses the etiological issues of treatment-resistant depression including genetic susceptibility, structural and functional MRI markers, neurogenesis, neuroinflammation and neuromodulation treatment for treatment-resistant depression. Section V highlights new perspectives of depression. Neurotrophic hypothesis-driven BDNF-TrkB signalling pathways and downstream of neurotransmitters have attracted attention to new pharmacologic targets. Homeostatic regulation of sleep, its dysregulation in mood disorders, and updated theories between inflammations and depression are discussed. The book will provide a better understanding of clinical and biological features and the management of depression, and will also function as a step onto the path toward the ultimate goal of predicting, preventing and treating depression.