Depression and anxiety are like the two sides of a coin in the history of mental illness, which is characterized by long episodes of sadness and hopelessness. Depression is a serious mental disorder among all the ages, which makes the patient to commit suicide and finally, it ends with big agony among the people. In the previous era, it was not notable, but the advancement in neuroscience has made a tremendous impact in the field of clinical investigations and the pharmacotherapy. Major depressive disorder, generalized anxiety disorder, and phobias are more common among the behavioral disorders, Brain imagining and various postpartum studies have revealed that the depression is precipitated by atrophy and irregular expression of a brain-derived neurotrophic factor in the brain and impairment of neural circuits. Hypothalamic Pituitary Adrenal Axis also contributes a major part in the symptoms of mood disorders. Genetic errors have disclosed the complexity by linkage studies and supported by monoamine deficiency in the brain. application of psychotherapy and medication has deleted the worst stages of depression. This review discusses about etiology, the classifications of depression disorders and the genetic inclination in mood disorders. It also reviews about the current diagnostic methods and global burden of the depression. © 2020 Elsevier B.V., All rights reserved.