The exact therapeutic mechanism of action of electroconvulsive therapy (ECT) remains unresolved. Numerous psychological theories from decades ago have been proven untrue. In the ensuing years, ECT has been proven to have numerous reproducible effects on brain chemistry, regional brain activity, electroencephalographic sleep stages, and neurogenesis. Clinically, ECT has been shown to have antidepressant, antipsychotic, antimanic, antiparkinsonian, and anticonvulsive effects. It is possible that different biological effects of ECT are responsible for different clinical effects or that several biological effects in concert work together to produce a given clinical effect. This paper comments on the array of possible mechanisms and points toward the future of mechanistic research in ECT.