Postpartum depression is a mood disorder that develops after the delivery of a baby. Depressive symptoms are comparable to those experienced in major depressive disorder in the general population and include dysphoria, anhedonia, hopelessness, weight changes, sleep disturbance, fatigue, and neurocognitive dysfunction. Given that changes in sleep, energy, and appetite are common in the typical postnatal period, the diagnosis of postpartum depression is often delayed or missed.

While a consensus on an exact definition of the postpartum period is lacking, many consider it to be the first 12 months after birth. Around 50% of patients will experience onset of symptoms before or during pregnancy. Of those who develop symptoms following delivery, onset typically occurs within the first months following parturition. With or without treatment, postpartum depression may resolve or may develop into a chronic depressive disorder. Patients remain at high risk of recurrence of depressive episodes.

Postpartum depression affects maternal-infant bonding and is associated with abnormal development and cognitive impairment in the children. The condition also may have negative effects on the mother's relationship with her partner and other children.

The strongest risk factor for postpartum depression is a personal history of depression (either perinatal or nonperinatal). Other risk factors include stressful life events, such as emigration or relationship conflict, and poor social and/or financial support during the perinatal period. Comorbid mental illness is common. Many other potential risk factors have been identified, such as young age, single marital status, and unintended pregnancy, although these are less well established.