This book leverages data from two major international large-scale assessments—the Trends in International Mathematics and Science Study (TIMSS) 2019 and the International Civic and Citizenship Education Study (ICCS) 2016—to investigate the extent to which education for sustainable development learning outcomes, such as environmental knowledge and willingness to act pro-environmentally, are achieved and fostered in various educational systems. This introductory chapter lays the foundation of this exploration, providing a comprehensive overview of the book’s conceptual framing, methodology, and structure, guiding readers through the subsequent chapters. Central to the book is the understanding of potential disparities in students’ environmental knowledge and their willingness to act pro-environmentally, both across and within nations. The book also examines the potential role of lower-secondary school learning opportunities in nurturing environmental knowledge and the intended behavior of young learners.