Over the years, attempts have been made to classify depressive syndromes based on various criteria. For several decades, the term reactive depression was used to describe cases involving an obvious precipitant, whereas endogenous depression lacked a recent stressor. Alternatively, the term secondary depression has been used in reference to cases related to a defined medical condition, as opposed to examples of primary depression. In the current classification scheme, the Diagnostic and Statistics Manual of Mental Disorders, 5th edition (DSM-V) lists fifteen distinct diagnoses related to disorders of mood, which are shown in Table 4.1. Eight of these disorders are considered depressive disorders, whereas seven categorize patients within the bipolar spectrum of illness.