Kurt Freund (17 January 1914 – 23 October 1996) was a Czech-Canadian physician and sexologist best known for developing the penile plethysmograph (a measurement of sexual arousal in males), research studies in pedophilia, and for the "courtship disorder" hypothesis as a taxonomy of certain paraphilias (voyeurism, exhibitionism, toucherism, frotteurism, and what he called "preferential rape").

In 1943, they divorced in order to protect Anna and their newborn daughter Helen from anti-Jewish and anti-miscegenation legislation implemented by the German Nazi Occupiers.

Freund then began plethysmography studies of male sexual orientation at the Centre for Addiction and Mental Health (then called the Clarke Institute of Psychiatry) in Toronto, where much of the research and published data using PPG originated.

Some of his patients voluntarily sought to change their sexual orientation, while others received remission of prosecution or legal penalties so that they could undergo the experiment.

Taking a behaviorist perspective, he attempted to reinforce heterosexual feelings while punishing homosexual ones in order to change sexual orientation.

Sex offenders could sometimes suppress arousal through concentration or surreptitiously causing themselves pain, similar to methods for producing false results on a polygraph (lie detector).

[11] There was controversy regarding potential abuses of devices to measure sexual interests, following fears that it might lead to discrimination against gay men.

[9][18][19] Freund was cremated, and his ashes were scattered on the lawn across from his office at the Clarke Institute in Toronto and on the grounds of Psychiatric Hospital Bohnice in Prague, where he had worked for many years in Czechoslovakia.