This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book addresses common criticisms of the application of experimental designs to education research and discusses reasons why they have not been applied in education as frequently as they have been in other fields. It provides a discussion of the circumstances under which experiments are most appropriate and offers ideas for how experiments can be combined with quasi-experimental and qualitative research methods to contribute useful information for education policy decisions. The book argues that experimental designs linked to nationally representative surveys are a strong combination because they address issues of prevalence, cause, and coherence across the education system and can help increase our understanding of school interventions in different contexts. It discusses the advantages of using growth mixture modeling to analyze longitudinal data in education.