This introduction to the Population, Space and Place Special Issue ‘Researching illegality and labour migration: the research/policy nexus’, considers what is meant by ‘illegal immigration’. This is of key importance to both policy and academic discussion, and contradictions and debates are evidenced in the terminology (‘illegal’, ‘irregular’, ‘undocumented’, etc.) deployed. The paper briefly reviews current academic literature and situates the issue's contributions within this. It concludes by drawing attention to migrant agency and its relation to labour markets and migratory networks. Copyright © 2010 John Wiley & Sons, Ltd.