The National Health Service was created at the end of the Second World War. Its structure has remained relatively stable until the 1970s. Since then, politicians have continued to reform it at an ever-increasing rate and, in 2012, the biggest change to the English NHS structure was implemented (Reynolds and McKee 2012). The question as to why the reforms are being undertaken is crucial. Growing demands, changing epidemiology, better understanding of the determinants of health, and evolving societal values have all influenced the process. Perhaps most crucial is the latter. It is probably more appropriate to describe the current NHS as four differing NHS care systems that are coterminous with the legislative bodies that exist within the UK, namely England, Northern Ireland, Scotland, and Wales. Not only are the planning arrangements becoming more divergent, but also the philosophical approach underpinning each system is beginning to follow very different paths. The NHS has almost never taken a typical theoretical planning approach but rather has evolved due to the wide range of factors and influences involved. These include the changing power of health care professions, the need to ration services, adoption of economic theory (market forces and the internal market), and, not least, changing governments with differing political stances. The importance of understanding the history of the service and the lessons of the past are that they inform the present and can provide an indication of how the future may look. This chapter outlines the major influences on the NHS since its inception, describes the major problems currently faced by the NHS, and provides an overview of the ways in which clinical services are currently delivered. It will not give a detailed description of the structure of the health service, not least as by the time the book is published a new structure will exist. The current structure of the health service in each of the four countries of the UK will be available on this book’s website, and updated as changes occur.