The main aim of this section is to conceptualize interactions between sexual partners and suggest prospects for prevention based on partner interactions within the context of cultural norms. Chapter 1 by Ferrand and Snijders, explains how social networks and norms are related to sexual behaviour. The relationship between the partners is viewed as part of a social network. In Chapter 2, Ahlemeyer applies systems theory from a sociological perspective to different intimate communication patterns. His co-author Ludwig shows how recent contributions from cognitive and social psychological theories help in understanding sexual behaviour that results from the interactions between partners. In Chapter 3, Bastard, Cardia-Vonèche, Peto and Van Campenhoudt draw from different sociological models in describing several social factors related to sexual behaviour. In the last chapter of this section, Van Campenhoudt and Cohen explore the forms of causality used by the preceding authors and suggest implications for explaining sexual behaviour related to the risk of HIV infection. Referring to the broad concept of causality, Van Campenhoudt and Cohen first discuss the differences between the epistemological, theoretical and methodological characteristics used by the authors to explain sexual behaviour. They then review how the different perspectives deal with various dimensions of sexual relationships: the situation, time, meaning, power, sexuality, emotion and risk taking.