Curative electroconvulsive therapy (ECT) remains a very useful treatment, still irreplaceable for some specific rare cases, as long as other brain stimulation methods, such as transcranial magnetic stimulation, remain experimental. ECT must be preceded by a rigorous evaluation of its therapeutic index, based on its advantages and risks compared with other potential treatments, in view of the patient's medical and psychiatric history. The principal indication is very severe depressive illness. In view of its efficacy and speed of action, ECT may be a first-line treatment for life-threatening depression and a second line treatment for patients with major depressive disorder who do not respond or respond incompletely to antidepressant drugs. ECT can be given to patients with catatonia, including as first-line treatment for some. ECT remains an important treatment option for depression in the elderly, especially those with depression and reversible dementia. Other indications classically considered, although for fewer patients and never as first-line treatment, are difficult-to-treat patients whose acute mania, mixed mania, schizo-affective state or schizophrenia has failed to respond to an adequate dose of psychotropic drugs and can be considered drug-refractory. It has also been used in Parkinson's psychosis and drug-resistant epilepsy. Preventive or maintenance ECT is appropriate for a few depressed patients who respond to it and it alone. It is the only effective option for these severely and recurrently depressed, medication-resistant patients. Some technical issues remain very empirical: seizure threshold determination, number of sessions, and concomitant pharmacotherapy. The practice of ECT must comply with very strict rules: information to and consent by the patient or family, performance at a hospital center by a team including a psychiatrist, anesthetist, and trained nurses.