Debates about migration are often in the news. People quote numbers about how many people are entering and leaving different countries. Governments need to plan and manage public resources based on how their own populations are changing.

Informed discussions and effective policymaking rely on good migration data. But how much do we really know about migration, and where do estimates come from?

In this article, I look at how countries and international agencies define different forms of migration, how they estimate the number of people moving in and out of countries, and how accurate these estimates are.

Migrants without legal status make up a small portion of the overall immigrant population. Most high-income countries and some middle-income ones have a solid understanding of how many immigrants live there. Tracking the exact flows of people moving in and out is trickier, but governments can reliably monitor long-term trends to understand the bigger picture.

Who is considered an international migrant? In the United Nations statistics, an international migrant is defined as “a person who moves to a country other than that of his or her usual residence for at least a year, so that the country of destination effectively becomes his or her new country of usual residence”.1

For example, an Argentinian person who spends nine months studying in the United States wouldn’t count as a long-term immigrant in the US. But an Argentinian person who moves to the US for two years would. Even if someone gains citizenship in their new country, they are still considered an immigrant in migration statistics.

The same applies in reverse for emigrants: someone leaving their home country for more than a year is considered a long-term emigrant for the country they’ve left. This does not change if they acquire citizenship in another country. Some national governments may have definitions that differ from the UN recommendations.

What about illegal migration? “Illegal migration” refers to the movement of people outside the legal rules for entering or leaving a country. There isn’t a single agreed-upon definition, but it generally involves people who breach immigration laws. Some refer to this as irregular or unauthorized migration.

There are three types of migrants who don’t have a legal immigration status. First, those who cross borders without the right legal permissions. Second, those who enter a country legally but stay after their visa or permission expires. Third, some migrants have legal permission to stay but work in violation of employment restrictions — for example, students who work more hours than their visa allows.

Tracking illegal migration is difficult. In regions with free movement, like the European Union, it’s particularly challenging. For example, someone could move from Germany to France, live there without registering, and go uncounted in official migration records.2 The rise of remote work has made it easier for people to live in different countries without registering as employees or taxpayers.

Immigrants increasingly face exclusion at the local level. How do they respond to such backlash? This paper examines how exclusionary local immigration policies influence immigrants' internal migration preferences---an understudied but key outcome in the relevant political debate. Drawing on two pre-registered survey experiments conducted among first-generation Mexican immigrants in the United States, I show that while such policies do shape preferences over whether and where to move, economic considerations often outweigh their effects. Importantly, exclusionary policies influence all classes of immigrants, including naturalized citizens who are not their direct targets. This is because concerns about safety and discrimination, in particular in places with exclusionary policies, are widespread among all classes of immigrants irrespective of legal status. The findings contribute novel empirical evidence to a contentious political debate and reveal how local immigration policies can affect not only immigrants but also American citizens and voters.

Dear State, Tribal, Territorial, and Local Government Partners, On February 19, 2025, President Trump issued an Executive Order titled “Ending Taxpayer Subsidization of Open Borders

.” As the Acting Assistant Secretary for Children and Families, I am committed to faithfully implementing the President's Executive Order. The Administration for Children and Families (ACF) at the U.S. Department of Health and Human Services provides federal leadership, partnership, and resources for the compassionate and effective delivery of human services to vulnerable populations to help families achieve prosperity and independence. Program eligibility rules are determined by Congress. In 1996, Congress passed the Personal Responsibility and Work Opportunity Reconciliation Act (PRWORA, P.L. 104-193) that generally prohibits illegal aliens from receiving Federal benefits, including Temporary Assistance for Needy Families (TANF), Child-Care, Low-Income Home Energy Assistance Program, Foster Care, Social Services Block Grant (SSBG). Title IV of the PRWORA states that “[i]t is a compelling government interest to remove the incentive for illegal immigration provided by the availability of public benefits.” Nearly three decades after enactment, the promise of PRWORA has been eroded. That ends now. Illegal aliens have already violated United States law and we will not be spending taxpayer dollars to take care of their needs. President Trump's Executive Order reaffirms this important national policy and puts the needs of Americans first. To implement the President’s Executive Order, ACF will use all available legal authority to end any incentives in human services programs that encourage illegal immigration. To that end, ACF is reviewing the public benefit programs we administer to ensure alignment with the President's Executive Order. Following that review, ACF will implement necessary changes so all its programs are consistent with Federal law, including PRWORA. ACF will also work to ensure that all information about program eligibility is accurate and does not serve as an incentive to encourage illegal migration. Furthermore, ACF will take all necessary measures to improve eligibility verification, deter fraud, and enforce the law by revoking grants to organizations that distribute benefits to illegal aliens in contravention of federal or state law. I look forward to working with State, Tribal, territorial, and local government partners to achieve the purpose of the President's Executive Order. I am confident its implementation will improve program integrity, exercise sound stewardship of taxpayer dollars, and better support our Nation’s children and families. Thank you for your continued work to help address the human service needs of vulnerable Americans. I welcome any ideas you might have in improving the administration of ACF programs and achieving alignment with the President's Executive Order.

Sincerely, Andrew Gradison Acting Assistant Secretary

Metadata-only record linking to the original dataset. Open original dataset below.

Context

Missing Migrants Project tracks deaths of migrants, including refugees and asylum-seekers, who have died or gone missing in the process of migration towards an international destination. Please note that these data represent minimum estimates, as many deaths during migration go unrecorded

What is included in Missing Migrants Project data?

Missing Migrants Project counts migrants who have died at the external borders of states, or in the process of migration towards an international destination, regardless of their legal status. The Project records only those migrants who die during their journey to a country different from their country of residence. Missing Migrants Project data include the deaths of migrants who die in transportation accidents, shipwrecks, violent attacks, or due to medical complications during their journeys. It also includes the number of corpses found at border crossings that are categorized as the bodies of migrants, on the basis of belongings and/or the characteristics of the death. For instance, a death of an unidentified person might be included if the decedent is found without any identifying documentation in an area known to be on a migration route. Deaths during migration may also be identified based on the cause of death, especially if is related to trafficking, smuggling, or means of travel such as on top of a train, in the back of a cargo truck, as a stowaway on a plane, in unseaworthy boats, or crossing a border fence. While the location and cause of death can provide strong evidence that an unidentified decedent should be included in Missing Migrants Project data, this should always be evaluated in conjunction with migration history and trends.

What is excluded?

The count excludes deaths that occur in immigration detention facilities or after deportation to a migrant’s homeland, as well as deaths more loosely connected with migrants´ irregular status, such as those resulting from labour exploitation. Migrants who die or go missing after they are established in a new home are also not included in the data, so deaths in refugee camps or housing are excluded. The deaths of internally displaced persons who die within their country of origin are also excluded. There remains a significant gap in knowledge and data on such deaths. Data and knowledge of the risks and vulnerabilities faced by migrants in destination countries, including death, should not be neglected, but rather tracked as a distinct category.

What sources of information are used in the Missing Migrants Project database?

The Missing Migrants Project currently gathers information from diverse sources such as official records – including from coast guards and medical examiners – and other sources such as media reports, NGOs, and surveys and interviews of migrants. In the Mediterranean region, data are relayed from relevant national authorities to IOM field missions, who then share it with the Missing Migrants Project team. Data are also obtained by IOM and other organizations that receive survivors at landing points in Italy and Greece. IOM and UNHCR also regularly coordinate to validate data on missing migrants in the Mediterranean. Data on the United States/Mexico border are compiled based on data from U.S. county medical examiners, coroners, and sheriff’s offices, as well as media reports for deaths occurring on the Mexican side of the border. In Africa, data are obtained from media and NGOs, including the Regional Mixed Migration Secretariat and the International Red Cross/Red Crescent. The quality of the data source(s) for each incident is assessed through the ‘Source quality’ variable, which can be viewed in the data. Across the world, the Missing Migrants Project uses social and traditional media reports to find data, which are then verified by local IOM staff whenever possible. In all cases, new entries are checked against existing records to ensure that no deaths are double-counted. In all regions, Missing Migrants Project data represent a minimum estimate of the number of migrant deaths. To learn more about data sources, visit the thematic page on migrant deaths and disappearances in the Global Migration Data Portal.

Content

What are the variables used in the Missing Migrants Project database?

This section presents the list of variables that constitute the Missing Migrants Project database. While ideally, all incidents recorded would include entries for each of these variables, the challenges described above mean that this is not always possible. The minimum information necessary to register an incident is the date of the incident, the number of dead and/or the number of missing, and the location of death. If the information is unavailable, the cell is left blank or “unknown” is recorded, as indicated in below.

1. Web ID - An automaticall...