Profound social and economic change in Eastern Europe and Central Asia has created conditions that make the countries in these regions particularly vulnerable to drug use and the spread of HIV. This booklet, aimed largely at policymakers and practitioners, presents an overview of lessons learned and challenges for the future. Examples from 11 countries (Belarus, Bulgaria, the Czech Republic, Hungary, Kazakhstan, Lithuania, Poland, the Russian Federation, Slovakia, Slovenia, and Ukraine) illustrate how drug abuse and HIV prevention strategies and interventions have been introduced into specific national and local contexts, and the responses to a number of important challenges. The case studies are grouped according to the focus of the project, as follows: fieldwork, political mobilization and strategy development, and training and networking. This collection shows the different adaptations that take place in response to local concerns, and also provides an up-to-date picture of the challenges commonly confronted in developing HIV prevention strategies among people who inject drugs.