The past three decades have been marked by significant progress in our understanding of the biological foundations of human behaviour, the evolutionary forces that drive human conduct and cognition and environmental factors that turn genes on and off. Concurrently, advances in communication technologies have drastically changed the way people meet and mate; demographic trends have modified patterns of supply and demand of potential mates while economic trends have affected men and women’s’ motivations for sexual partnering.

Consequent changes in sexual values, attitudes and norms; sexual behaviours including sexual practises; and concepts of marriage, commitment, love and sex have been remarkable. Major trends in sexual behavioural determinants of sexually transmitted infection spread include: exponential increases in the size of sexual core groups; increased acceptance of commercial and transactional sex; increases in male, female and underage sex tourism; and increased geographic mobility of sex workers. These trends result in greater connectedness among sexual core groups across national boundaries thereby limiting the effectiveness of national prevention programmes. Moreover, both increased sexual mixing between core groups and the general population and increased reporting about sexual core behaviours through social media facilitate behavioural contagion and enhance the impact of sexual core groups on the behaviours of the general population. It is surprising that STI are not spreading faster globally in light of these changes in their social and behavioural determinants.