This introduction presents an overview of key concepts discussed in the subsequent chapters of this book. The book sets out to achieve three aims in relation to education policy research and theory: it argues for the utility and necessity of theory; it celebrates the pleasures and rewards of theory; and, it offers models of, and advice on, the use of theory in education policy research. The aims of critical policy studies are always in need of being renewed, reinvented and rejuvenated; and indeed, this book presents some examples of theory being used to reinvigorate enduring problems of education policy studies. The book then shifts to 'policy sociology' that places 'policy' at the centre of analysis, to 'assemblage ethnography' where the assemblage offers new analytic potential by situating policy processes in wider forces of assemblage and disassembly. The book breaks down the key components of governmentality: pastoral power, security, and self-governance.