This is the introductory chapter of the book presenting the first findings from the fourth sweep of the International Self-Report Study (ISRD4), an ongoing multinational project examining young people’s experiences with victimization and offending. Covering 21 countries, we report results for approximately 58,000 adolescents aged 13–17. After introducing the ISRD study, this chapter presents the methodology of the ISRD4 study, including a description of the sample. We describe the controls used to filter out problematic responses to the survey and maximize the quality of the data. One of the virtues of the ISRD project is its multinational character, allowing comparisons between countries. The chapter shows that some variation between countries could be based on different magnitudes of problematic responses to the survey, implying that caution needs to be exercised when comparing the prevalence of victimization or offending between countries. We describe the two approaches that we take to comparisons of victimization and offending between countries, one being the clustering of countries based on the characteristics of their market economy and the other using country-level scores to examine the relationships between selected variables of interest. The chapter concludes with an overview of the remainder of the book.