This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book provides a vivid sense of the way case studies actually happen, how the researcher and the setting interact, and how insight is gained. It looks at the antecedents of teacher classroom activity in their plans, and in the recommendations of the teacher guides. The book considers the costs and rewards of innovation from their readings of extensive interviews with teachers. It also looks at the concept of teachers' classroom influence as it is involved in change. The way an integrated science curriculum was modified is explained in terms of teacher conservation of influence at the expense of conformity to project plans. The book suggests that the expectations that reformers have had for change in schools in recent decades reflect an inadequate, mechanistic conception of institutional life.