It is difficult to estimate the size of the irregular migrant population in a specific city or country, and even more difficult to arrive at estimates at the European level. A review of past attempts at European-level estimates reveals that they rely on rough and outdated rules-of-thumb. In this paper, we present our own European level estimates for 2002, 2005, and 2008. We aggregate country-specific information, aiming at approximate comparability by consistent use of minimum and maximum estimates and by adjusting for obvious differences in definition and timescale. While the aggregated estimates are not considered highly reliable, they do -- for the first time -- provide transparency. The provision of more systematic medium quality estimates is shown to be the most promising way for improvement. The presented estimate indicates a minimum of 1.9 million and a maximum of 3.8 million irregular foreign residents in the 27 member states of the European Union (2008). Unlike rules-of-thumb, the aggregated EU estimates indicate a decline in the number of irregular foreign residents between 2002 and 2008. This decline has been influenced by the EU enlargement and legalisation programmes. © 2011 The Authors. International Migration © 2011 IOM.

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education economics psychological aspect demography Europe Population Dynamics human statistics Population Groups Statistics as Topic population decline ethnology ethnic and racial groups population size Humans History, 21st Century European Union Article history migration legal aspect Transients and Migrants