Depression is increasingly recognized as a highly recurrent and potentially chronic illness that imposes a substantial burden on individuals, families, and society. Evidence indicates that the risks of depressive recurrence, treatment resistance, and chronicity increase as the illness becomes more highly recurrent. Up to 1 year of continuation phase therapy is now recommended for virtually all depressed patients who respond to antidepressants, with a longer course of maintenance phase pharmacotherapy recommended for those who have experienced multiple episodes. Antidepressants, when effective during the acute phase of therapy, reduce the risk of depressive relapse (continuation phase) and recurrence (maintenance phase) by at least 50%. Longer-term antidepressant pharmacotherapy is most effective when the full dose of medication effective during acute-phase treatment is continued. As combined treatment with antidepressants and psychotherapy may improve shorter-term outcomes for patients with more severe recurrent depression, ongoing combined therapy may be indicated, especially for patients at particularly high risk. Approximately 5% to 10% of patients maintained on antidepressants relapse yearly, leading some to implicate tachyphylaxis. However, before attributing relapse or recurrence to diminished responsiveness to antidepressant medication at the neurochemical level, clinicians should ensure that the patient has been adherent to therapy as prescribed and consider other explanations.