The United Nations Statistics Division collects data on flows and stock of migrants through the Demographic Yearbook data collection system. Overall, sixteen tables on international migration statistics are collected by the Demographic Yearbook. This is done by requesting countries to provide data by completing data questionnaires.

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It has 11 tables, containing data on inflow/outflow of foreigners/citizens and incoming/departing migrants by purpose, duration, country of birth and/or citizenship.

Some of these are cross-tabulated by age and/or sex.

Two other questionnaires request data on international migrant stock collected from population censuses. These are:

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The above two questionnaires together contain 5 tables, pertaining to the characteristics of international migrants, such as age, sex, country of birth, country of citizenship and occupation.

Data dissemination

Detailed statistics on international migration flows and stock have been published by the United Nations Statistics Division in two issues of the Demographic Yearbook: 1977 and 1989. Two other issues of the Demographic Yearbook, published respectively in 1985 and 1994, include a limited number of tables pertaining to international arrivals and departures.

Data on migrant stock collected from national population censuses for the 1990 round (1985-1994) and the 2000 round (1995-2004) of censuses are available in electronic format on the Demographic Yearbook Special Census Topic Volume 3: International Migration Characteristics.

Based on our collection of national census questionnaires, UNSD compiled a database of census questions on the following three topics from the 2000 census round (1995-2004):

-	Country of birth
-	Country of citizenship
-	Year or period of arrival

A review of data collection and dissemination

A technical report was produced in 2004 to review the collection and dissemination of international migration statistics at the United Nations.