When the epidemics of HIV and AIDS were first detected little was known about patterns of sexual behaviour in different European countries beyond that attributable to conjecture and stereotype. Relatively few countries had conducted population surveys of young people’s and adult’s sexual behaviour, and the data that was available was most usually non-comparable. This was unfortunate in so far as forward planning for the prevention of HIV was concerned. It also posed problems for the development of a European strategy against AIDS sensitive to the needs of particular countries and areas. Thankfully, the European Concerted Action on sexual behaviour and the risk of HIV infection, whose work is reported in this book, took place, since for the first time it allowed a comparative analysis of data collected in 11 countries. Here we find the fruits of over seven years labour. Scientific information about the prevalence of different kinds of sexual behaviour is analyzed in ways relevant to a better understanding of the epidemic and its dynamics. Among the issues examined are sexual debut, the reported prevalence of different sexual practices, patterns of homosexuality and bisexuality, reported rates of sexually transmitted diseases, reported condom use and other forms of prevention. Behavioural data is complemented by an analysis of social representations of HIV and AIDS, attitudes towards the syndrome, and factors influencing discrimination and stigmatization. In a significant number of respects therefore, this is a truly remarkable book. The challenge now lies in developing programmes and interventions that build upon what we have learned, and in focusing our work so as to meet the real, rather than the imagined, needs of different countries, communities and groups.