For foreign nationals in Belgian detention centres to be able to return to their country of origin or to another country where they are allowed to stay, they must have the necessary travel documents. The objective of the Immigration Office is to reduce the detention period as much as possible. Early identification is paramount in shortening the return process and the possible detention associated with that process.

An identification should result in issuing a travel document (the laissez-passer) allowing a third-country national's return.

If, based on the identity documents, there is no doubt about the identity, the Immigration Office can sometimes issue a standard travel document. The basis for this practice is contained in the agreements concluded between Belgium or the European Union and a . The identification procedure will then end with issuing an "EU laissez-passer".

In practice, foreign nationals in irregular stay do not have or conceal these documents, do not want to cooperate in their identification or simply give false information in order to complicate the execution of the .

The first step in the identification process is to convince the foreign national to present their identity documents. If the foreign national in question still has a valid passport, this will automatically reduce the period of detention before returning. If they do not, they will be interviewed to obtain the necessary identity and nationality details and any helpful information that helps to determine their real identity. The person concerned will also be asked to fill in questionnaires provided by Belgium, the country's authorities of which they claim to be a national and those relating to the various existing readmission or administrative agreements signed by Belgium and the country of origin.

The embassies or consulates of the countries of origin in Belgium or the competent authorities in the country of origin play a significant role in identifying a foreign national in irregular stay. It is in everyone's interest that the cooperation between the Immigration Office and the competent authorities of the country of origin is optimal. The Immigration Office relies in particular on the help of diplomatic and consular representatives to assist its agents, convince foreign nationals in irregular stay that it is in their interest to cooperate in the identification process, respect Belgian and European laws and directives and comply with the orders to leave the territory that are served on them.