Any attempt to account for the wide range of sexual behaviour and of prevention strategies adopted by individuals must go beyond a purely individualistic perspective. Sexual practices take place within the wider context of social representation, even if behaviour is not always coherent with associated social representations. In this paper the normative framework of sexual behaviour is studied in relation to several examples: norms relating to love and to sexual relationship; the social representation of faithfulness, of the condom. and of the content of the sexual act; behavioural changes envisaged in relation to the Aids epidemic, perceptions of and recourse to the HIV screening test. Clear differences in social representation occur between men and women; for example, the latter are more critical of infidelity. Consideration of the normative context of individual behaviour can contribute to the definition of prevention policy.