The concept of ‘irregular migration’ is commonly used to describe a variety of phenomena involving people who enter or remain in a country of which they are not a citizen in breach of national laws. The analysis of irregular migration is further hampered by a serious lack of accurate data, making it difficult to identify trends or to compare the scale of the phenomenon in different parts of the world. It is possible to compare different sources of recorded migration data and population data to highlight discrepancies that might be accounted for by irregular migration. Irregular flows pose challenges of control and management, as well as concern for the safety and dignity of migrants on the move. People who move in an irregular fashion leave their countries for exactly the same reasons as any other migrants. In political and media discourses, irregular migration is often described as constituting a threat to state sovereignty.