them in as transparent a fashion as possible so that readers may choose the version which best suits their needs.

The first version simply contains the raw data with some minor adjustments and will be of more use to a demographer. The later versions contain more bilateral entries, and despite the fact that individual entries are less accurate (some, indeed being pretty crude approximations), they may well prove more useful to the applied economist. The final version (version 4), though covering only the foreign-born, represents as full a picture of bilateral international migrant flows as data permit. By introducing the data in this way, it is hoped that this paper will provide a pathway into a rich resource for further research.<sup>3</sup> The data in the four matrices are generated by the stock of migrants at destination country and territory disaggregated by country and territory of origin around the year 2000. They make no reference to the time at which a migration has taken place, but provide only an estimate of the cumulative migrations to date into an area (net of reemigrations). At present, no global source exists for flow data in which immigration (or emigration) can be related to specific periods of time, for example, movements over the previous 1 year or 5 years. Flow data of this type are only available for a relatively few, generally more developed, countries. In a way, international migration statistics are not far from where data on internal migration were some 40 years ago.

The paper concludes with a brief description of the patterns that are revealed by this new data source. The most important finding is that patterns do indeed differ substantially across migration corridors. For example, immigration in the United States is dominated by Latin America, whereas Western European immigration draws heavily on Eastern Europe, Central Asia and the Mediterranean region. Over one-third of world migration is from developing to developed countries, with only about a quarter between developing countries. Intra-developed country and intra-FSU (former Soviet Union) flows each account for about 15 percent of the total. Over half of migration is between countries with linguistic ties. Africa accounts for 8 percent of Western Europe’s immigration and much less of that in other rich regions.

The remainder of the paper comprises the following. Section 2 describes who qualifies as a migrant under both of the definitions utilized in this paper. Section 3 investigates the sources of migration statistics and their interpretation; it makes clear the heterogeneity that exists among the available statistics and the challenges entailed in making them comparable.<sup>4</sup> Section 4 outlines the different versions of the matrices and the final section provides some summary statistics of the patterns observed.

# **2. Who Counts as a Migrant?**

Definitions of a “migrant” are various. International migrants may be recorded in terms of:

- country of birth

- country of citizenship

- last country of previous residence

> 3 The database has undergone several rounds of improvement and extension. The first public version was described in Parsons et al (2005) and an intermediate version was used and briefly described in Ratha (2006).

> 4 Our treatment is far from comprehensive. See Bilsborrow et al (1997).

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