Major depressive disorder (MDD) is manifested by mood, behavioural, cognitive, and somatic symptoms. This is reflected in the diagnostic criteria of both DSM-5 and ICD-10. Differential diagnosis typically includes the consideration of other mood and psychiatric disorders, neurological, medical and genetic conditions, as well as bereavement. Diagnostic investigations are commonly combined with the evaluation of functioning since the vast majority of MDD patients experience functional impairment. Suicidality is a major challenge in the management of MDD. Rigorous risk assessment, minimisation of risk factors, and promotion of protective factors are essential in suicide prevention. Treatment strategies can be split into acute, continuation, and maintentance phases. Depending on depression severity and other specifiers (e.g., psychosis, risk) both pharmacotherapy and psychotherapy can be efficacious first-line treatment options. Switching or augmenting initial treatment can be considered for non-responders. For continuation and maintenance phases, the primary aim of treatement is prolonging remission, preventing episode recurrence, and restoring psychosocial functioning.