Depression is a complex disease. Our knowledge about its pathogenic mechanism is still limited because it is a multifactorial disorder with diverse causes. Still, our understanding of the pathogenesis and mechanism of depression has dramatically improved over the last decade due to technological advancements. Now we have mounting data like brain imaging studies showing the functional brain anomalies of patients with depression, genetic studies showing genetic mutations, and other contributing factors from molecular biological studies, gene manipulation tests, and research done in the introduction and development of antidepressants