The 9th Annual Conference on Drug Use and Drug Policy, organized by the [Departamento de Ciencias de la Education de la Universitat de les Illes Balears] Education Department of the Balearic Islands University and the European Social Science Research Group on Drug Issues; under the sponsorship of the [Delegacion del Gobierno para el Plan Nacional sobre Drogas] Government Office for the National Drugs Scheme, [la Conselleria de Sanitat i Consum del Govern Balear] Balearic Government Health and Consumption Council and [Sa Nostra, Caja de Baleares] 'Sa Nostra' Balearic Savings Bank was held in Palma de Mallorca at the end of 1998. In the a forementioned conference, which was attended by researchers from Universities and Research Centres in Europe and the United States, two main themes were dealt with: on the one hand, the analysis of drug use in different countries, and on the other hand the policies for dealing with the treatment of drug dependency and their assessment, by way of different methodologies and approaches. From the analysis of the different papers presented - which were of a great scientific, methodological, professional and social interest - a series of conclusions can be drawn that could lead to debate in a wide range of professional, political and academic circles, in which the issue of drug dependence is a particularly significant, important, subject. Thus, it is worth highlighting a series of reflections: first of all, the need and importance of carrying out epidemiological studies which, in a serious, rigorous way, would enable us to have profound knowledge on a subject which is difficult to gain an overall view of. In this way, it is interesting to analyse and reflect on the methodological approaches posed. Secondly, the studies presented on the different treatments of drug dependency, their results and the systems of evaluation applied in order to find out the effects and the whys and wherefores of the same are also very interesting. Thus, it is necessary to give a brief description of the comparative studies between the different treatments with the use of substitutes and their consequences and results, at different levels. (Editor' s abstract)