This lecture will focus on what we know currently on major depressive disorder, from its clinical manifestations to its epidemiology and risk factors. The heterogeneity of major depressive disorder will also be discussed, with a focus of several subtypes, including melancholic and atypical depression. A review of existing treatment options will be provided, followed by a discussion on the current limitations of existing pharmacological treatments. Finally, the lecture will review the new pharmacological therapies that have merged in the past few years and that reflect the discovery of novel molecular targets.