A from of treatment considered outmoded around the turn of the century, suggestion now plays a considerable role in general medicine and all contemporary psychotherapies—including psychoanalysis, behavior therapy, and group encounters. The return of suggestion is dramatically seen in the community mental health movement, in which centers dispense brief therapy, help and advice to large portions of the population previously unreachable. In spite of the ubiquity of suggestion and the large literature that developed at the end of the 19th and the beginning of the 20th century, very little is actually known as to how it “works”, if and when it does. Considerably more research is needed on the subject, which stands out as a basic riddle of the behavioral sciences.