3,4-methylenedioxymethamphetamine (MDMA) is a substituted phenethylamine that became popular as a recreational drug (ecstasy) and therapeutic tool during the late 1970's and early 1980's. Escalating recreational use led to its prohibition, but scientific interest in the drug has persisted due to its unique prosocial effects. Under clinical observation, volunteers report that MDMA increases feelings of closeness towards others, empathy, and sociability. In addition to these acute effects, there is accumulating evidence that MDMA can have powerful and enduring therapeutic benefits.