Until recently, Quebec was the first to have regulated the practice of psychotherapy through law adopted in 2009. The law emerged following 30 years of efforts and inter-professional discussions that led to a consensus by an expert committee presided by Dr Jean-Bernard Trudeau in 2005. In this essay, Dr Jean-Bernard Trudeau, general practitioner, and two psychiatrist and psychologist colleagues, who have participated to the expert committee or have been involved more recently in the implementation of law no 21 in Quebec, relate the main landmarks and moments in the regulation of the practice in psychotherapy following this inter-professional consensus that was translated in the law 21. They relate particularly the last ten years that have led to the adoption of law 21 in 2009, following two parliamentary commission after the Trudeau report. They underline how the practice of psychotherapy is integrated in the professional system and submitted to strict regulation. It includes regulations for obtaining the license of psychotherapist and for maintaining competence. Guidelines emerging from continuous inter-professional discussions for the application of the law and of its regulation in the public and private sectors are produced by the Quebec Professions Office. The definition of psychotherapy that was reached by consensus is not limited to the treatment of mental disorders and is distinguished from other intervention in the area of human relations. Continuous training is mandatory and is implemented on one hand by the Order of the psychologists for the psychologists and other professionals practicing psychotherapy and on the other hand the College of physicians for physician practicing psychotherapy. The authors finally described the interdisciplinary advisory council for the practice of psychotherapy that the legislator has foreseen as an external mechanism to insure the conformity of regulation with the spirit of the law and to give opinions to the various professional orders.