It is generally acknowledged that the undeclared economy lowers the quality of work and working conditions, undermines the business environment through unfair competition, and puts at risk the financial sustainability of social protection systems. Clearly, therefore, undeclared activities should not merely be discouraged, but should rather be transformed into regular work. The study on undeclared work-conducted by Sheffield University and Regioplan- shows that in advanced economies the size of the undeclared economy varies widely – from less than 10% in countries such as the US, the UK, Japan and the Netherlands to more than 25% in parts of southern and eastern Europe.