The focus of this book is to discuss teaching quality across the Nordic countries drawing on video data and student perceptions data from lower secondary students and classrooms across all five Nordic countries in three subject areas: mathematics, language arts, and social science education. In this introduction chapter we discuss and define how we use the term teaching quality in the current book and how it aligns with related terms such as effective teaching, good teaching as well as associated aspects such as equity and equality in teaching. In addition, we consider dilemmas and challenges when using large scale personally identifiable data such as video data and why the Nordic countries represent an ideal context for investigating teaching quality. We then outline the overall research design and methods applied, including the comparative ambition, and possible limitations. In the last section we discuss the composition of the book including a brief outline of the different chapters.