Margaret Thaler Singer was an American clinical psychologist and researcher with her colleague Lyman Wynne on family communication. She was a prominent figure in the study of undue influence in social and religious contexts, and a proponent of the brainwashing theory of new religious movements.

Brainwashing, also known as mind control, menticide, coercive persuasion, thought control, thought reform, and forced re-education, is the concept that the human mind can be altered or controlled by certain psychological techniques. Brainwashing is said to reduce its subject's ability to think critically or independently, to allow the introduction of new, unwanted thoughts and ideas into their minds, as well as to change their attitudes, values, and beliefs.