This report is the Irish contribution to an EU-wide investigation of illegal immigration and State approaches to illegally resident immigrants. There are two categories of illegal immigrant discussed in the current report: persons who enter the State illegally and continue to reside illegally and persons who enter legally and whose residence status later becomes irregular. Almost no statistics exist on stocks of illegally resident immigrants beyond the number of outstanding deportation orders. In this report we investigate legislative and policy approaches to the prevention of illegal immigration. A major source of illegal immigration to Ireland is a result of movements from within the Common Travel Area that Ireland shares with Britain. The available information on the social and economic situation and political participation of illegal immigrants is also presented.