Migration from one country to other is an outcome of war, ethnic, religious or linguistic discrimination and sometimes persecution of a particular community in a country or wide gap among countries in level of development, better employment opportunities and living conditions. Though many developed and fast developing countries are facing the problem of illegal migration, but India is worst hit in illegal immigration with more than 10 million illegal immigrants mostly from its eastern front bordering Banladesh. Now a new stream of illegal immigrants Rohingya from Myanmar had started entering in large numbers in India. As per National Registry of Citizen (NRC) around 40,00,000 illegal Bangladeshi immigrants are there in Assam alone. Top 10 worst hit countries due to illegal immigrants are 

1. India with more than 10 millions illegal immigrants

2. USA with about 10 millions illegal immigrants

3. Russia with more than 10 millions European and Asian especially Chinese illegal immigrants

4. U K with around 5,50000 to 9,50000 illegal immigrants

5. Germany with around 1,00,000 to 1 millions illegal immigrants

6. Malaysia with about 8,00,000 millions illegal immigrants

7. Brazil with about 7,00,000 illegal immigrants

8. South Korea with more than 1,70,000 illegal immigrants

9. Phillippines with about 1,00,000 illegal immigrants mainly from China

10. Cnada with 35000 to 1,20,000 illegal immigrants

Though some developed country with aging population or low population density may welcome illegal immigrants due to economic reasons, but a over populated country like India definitely suffers a lot due to illegal immigration. Illegal migrants put pressure on limited resources and create law and order problems due to unemployment and poverty. In certain areas where concentration of illegal immigrants are very high, they have created threat to local culture as it happened in Assam.

The reptriation of illegal immigrant is very difficult, because emigrant countries normally do not accept illegal immigrant as their own citizens, and this becomes even more difficult, if a strong and pragmatic bi-lateral treaty is not there between emigrant and immigrant countries on this issue. Therefore, fencing of border and stringent survillience is only way out to check illegal immigration.