This paper puts forward a French-British comparative approach of teacher identity. In each country, teachers have to take on complex missions, thus getting more and more torn between professional cultures which are the clore of their activity, and the urge to widen their range of action, disturbing the professional norms in use and blurring their original missions. To understand the construction of teacher identity nowadays, one has to go from functionalist problematics of acculturation to a constructivist one of subjectivation.