The demands for data on migration arising from the 2030 Agenda for Sustainable Development have prompted the international statistical community to review the use of traditional sources for migration data, such as population and housing censuses, household surveys and administrative records. There is also increased interest in looking for alternative sources to enhance the collection and analysis of migration data. Better use and understanding of existing data sources is essential to improve migration management and policy. Information about migration comes from a variety of data sources that have strengths and limitations and can be used to produce different migration statistics.

Remittances, usually understood as the money or goods that migrants send back to families and friends in origin countries, are often the most direct and well-known link between migration and development. Remittances exceed official development aid but are private funds. Global estimates of financial transfers by migrants include transactions beyond what are commonly assumed to be remittances, as the statistical definition used for the collection of data on remittances is broader (see IMF, 2009). Also, such estimates do not cover informal transfers. Remittances can also be of social nature, such as the ideas, behaviour, identities, social capital and knowledge that migrants acquire during their residence in another part of the country or abroad, that can be transferred to communities of origin (Levitt, 1998: 927).

Migration flows data capture the number of migrants entering and leaving (inflow and outflow) a country over the course of a specific period, such as one year (UN SD, 2017). Data on migration flows are essential for understanding global migration patterns and how different factors and policies in countries of origin and destination may be related to flows. However, in contrast to migration stocks data, estimates on migration inflows and outflows by country of origin and destination are not available at the global level. Currently, only 45 countries report migration flow data to the United Nations (UN DESA, 2015).  Migration flows data on migrants entering and leaving over the course of a given time period (usually a calendar year) are often confused with migration stock data which estimate all migrants residing in a country at a particular point in time (UN SD, 2017, emphasis added).   

International migrant stocks are estimates of "the total number of international migrants present in a given country at a particular point in time" (UN SD, 2017: 9, emphasis added). United Nations (UN) data on these stocks are based mostly on the country’s population that is born abroad, and (where this information is not available) on holding a foreign citizenship (UN DESA, 2016: 4; UN SD, 2017).  Data on migrant stocks are often reported together with data on migrant flows. Although both terms account for the number of migrants, what they measure is different. Migrant flows data account for the number of migrants entering or leaving during a specified time period (usually one calendar year), (UN SD, 2017).