To immigrate is to enter and settle in a country or region to which one is not native.
1. To move from one country or region and settle in another.
2. To change location periodically, especially by moving seasonally from one region to another.
Migrate, is used of people and animals and implies a lack of permanent settlement, especially as a result of seasonal or periodic movement.
Emigrate and immigrate are used only of people and imply a permanent move, generally across a political boundary.
Emigrate describes the move relative to the point of departure: After the Nazis came to power in Germany, many scientists emigrated (that is, left Germany).
Immigrate describes the move relative to the destination: The promise of prosperity in the United States encouraged many people to immigrate (that is, move to the United States).
Source: inside education yahoo