This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book examines the changing patterns and effectiveness of British military intelligence since the 1970s. In the last 40 years intelligence studies has become an important field in its own right, but much of the focus has been on civilian intelligence, and intelligence in North America. It concentrates on operational intelligence (OPINT) which can be seen as combining two areas: force protection and force projection. Force protection might also be classed as counter-intelligence and is clearly operationally crucial since without this any deployment is immediately vulnerable. The book discusses the ethical issues raised by military intelligence operations in various theatres. It examines the development of military intelligence in Northern Ireland, Iraq and Afghanistan, focusing on the development of the tactics, the effectiveness of the tactics employed and the ethical issues raised by their use.