The present article describes and analyses the emergence and development of a professional field called social integration. Ideas, theories, and occupational practices forming this field are explored, particularly those related to the development of a new discipline, that of psychotherapy. The development of three occupations (psychiatry, psychology and social work) and their professionalisation is described through their qualitative and quantitative take‑offs in particular historical periods. Three periods are identified: formation, 1850-1920, when psychiatry was defined as a medical sub-discipline; consolidation, 1920-1945, with the institutionalisation of psychiatric care, and with psychoanalysis and mental hygiene as qualitatively new cognitive bases for practitioners; and professionalisation, 1945-1980, with the deinstitutionalisation of psychiatric care and the professionalisation of psychologists and social workers. New ideas on subjectivity and individualism, new welfare state institutions, as well as collaborative professionalism all favoured the creation of psychotherapy as professional knowledge, and a possible new profession of psychotherapists.