Major depressive disorder is a multifactorial psychiatric disorder, in which different genetic, epigenetic and environmental factors play a causal role. We discuss novel findings in the genetics and epigenetics of depression, with special emphasis on the role of the brain derived neurotrophic factor (BDNF). Many stud¬ies show changes in BDNF levels as a result of treatment for depression, including as a result of treatment with non-brain stimulation. We highlight the role of BDNF as a possible biomarker of depression and an indicator of treatment response to antidepressant medication or non-invasive brain stimulation