Abstract
A "didactical contract" is an interpretation of the commitments, the expectations, the beliefs, the means, the results, and the penalties envisaged by one of the protagonists of a didactical situation (student, teacher, parents, society) for himself and for each of the others, a propos of the mathematical knowledge being taught. The text focuses mainly on didactical and ethical responsibility, paradoxes of the didactical contract, observation of the reactions of teachers to difficulties, explanation of long-term effects and extensions.