The pervasiveness of unelected bodies wielding official powers in the structures of modern democratic societies comes as a surprise to many. Their growth has been gradual and justified largely on a case-by-case basis. The total number is rarely added up. In the UK, where a comprehensive list is now provided, it has been estimated that there were at the end of 2004 over 650 ‘public bodies’ outside central government departments. The majority of these (around 400) were in the business of providing advice to government departments and a further 20 were bodies involved in Britain's national health service. This still left about 250 bodies with executive responsibilities. Of these, it has been separately estimated that around 120 have regulatory functions.

The rise of the unelected is an international phenomenon. In the United States two main waves of agency creation are usually identified – agencies created in the 1930s under the New Deal and agencies created in the 1960s and 1970s. A current tally lists over 1,000 federal agencies, of which the large majority were located within the executive branch, but around 200 were listed as independent or were more loosely attached. In the case of Sweden there are over 100 official agencies (excluding temporary advisory committees) and in the Republic of Ireland over 60 agencies and statutory independent bodies.

Different terminology is used to describe the bodies.