The official population of Moscow is based on those holding "permanent residency". According to Russia's Federal Migration Service, Moscow holds 1.8 million official "guests" who have temporary residency on the basis of visas or other documentation, giving a legal population of 13.3 million. The number of Illegal immigrants, the vast majority originating from Central Asia, is estimated to be an additional 1 million people, giving a total population of about 14.3 million.