Singer began to study brainwashing in the 1950s at Walter Reed in Washington, DC, where she interviewed United States soldiers who had been taken prisoner during the Korean War. Beginning in the late 1960s, she expanded her studies in the field of cults and published a number of articles on mind control ("psychological coercion") and similar areas. She developed theories about how cults recruit and retain members (such as her Theory of Systematic Manipulation of Social and Psychological Influence) and was on the board of many of the major anti-cult groups and organizations in the US. At one point, Singer interviewed Charles Manson.