reconstruct how denunciation took place, and the development of the climate of social betrayal which was encouraged by the inquisitorial authorities. We have identified the informants —old Christians— and those denounced —Jewish converts— and their respective socio-professional occupations. The informants were extremely intolerant of their Jewish converso neighbours, whose attitudes they monitored. They used the new horizontal mechanisms for social control, implemented, disseminated and encouraged by the inquisitorial authorities, which encouraged old Christians to observe, monitor and report dissident behaviour and practices among Jewish converts in Valencia.