The major objective of research conducted in medical science is to improve health. Health can be improved by prevention of diseases and treatment of diseases. One strategy to improve treatment is to optimise the choice of treatment suitable for individual patients. This feature of identifying suitable treatments for individual patients on the basis of certain characteristics is known as "precision medicine" or "personalized medicine". This technique of selecting a particular treatment for a particular individual leads to reduction in costs and side effects and also causes improved outcomes. The uniqueness of this technique lies in the fact that a particular treatment relevant to patient's characteristics is employed rather than treating the patient on the basis of clinical trial outcomes, in which the "average" improvement in the sample is used to know about the efficient or relevant treatment. The major application of personalized medicine has been found in dealing with the increasing medical cases of cancer, infectious diseases and cystic fibrosis.Major impact of personalized medicine is observed in curing of breast cancer, differentiating between tumours with and without high estrogen or epidural growth factor receptor expression is exploited to select relevant chemotherapeutic agents, such as tamoxifen and trastuzumab and also to avoid certain agents in isolation or combination when certain combinations of receptors are present.Generally, these particular treatments can be applied if one possesses deep knowledge of several pathophysiologies associated with a disease. This approach of personalized medicine is of great significance for the diseases characterized by syndromes, for which different etiopathological mechanisms are assumed to generate a similar clinical phenotype. An example of such varying or heterogeneous syndromes is Major Depressive Disorder (MDD). Plenty of research work conducted to subcategorize MDD has been in vain so far and thus a lacuna in reliable and distinct pathophysiologies still persists. MDD is one of the chief causes of disability in the world.Considering MDD as a rapidly growing health problem, this thesis is meant to identify the optimal or best suitable biomarkers for MDD characterization so as to enable early diagnosis of the disease.