Prior to the advent of the NHS, most hospitals were private in sense of being independent and self-governing. There were at that time a number of ‘municipal’ as opposed to purely ‘voluntary’ hospitals, but it is probably true to say that there was a charitable element in the funding of all hospitals, dating back to medieval times and perhaps even before. The idea of the profit-making hospital is relatively modern, though it is rapidly increasing in importance in the UK, as its share of the amount of private treatment undertaken demonstrates. The revenue earned by non-profit-making or charitable hospitals in excess of operating costs is usually reinvested in the hospital or the group of which it is part.