The glossary to understand and take action

A1 Certificate

The A1 certificate confirms the social security legislation applicable to a person in certain situations involving European mobility.

Démarche et formalité · Luxembourg Fiduciaries Editorial Team · Reviewed on

Understand the scope

What is this process for?

It does not by itself determine salary taxation, the right of residence or work authorisation. Posting and activity in several States must be classified according to their conditions.

In your file

How to prepare the process

The A1 document confirms the social security legislation applicable in situations covered by European coordination. It does not replace either a work permit or posting formalities under labour law. The analysis depends on the places and arrangements of work, particularly in the case of activity in several States. A change in circumstances may require a new assessment by the competent institution.

A scenario to help you understand

Educational example

An employee temporarily works for a client abroad: the employer reviews the A1 and, separately, the local obligations relating to that assignment.

Fictitious situation, presented to illustrate the concept.

Prepare for what comes next

Points to check

  • Décrire tous les pays d’activité
  • Distinguer sécurité sociale et droit du travail
  • Signaler les changements de situation

The practical question

Find out more

L’A1 permet-il à lui seul de détacher un salarié à l’étranger ?

Il concerne la législation de sécurité sociale applicable. Les obligations de droit du travail, de déclaration locale et de séjour ou travail doivent être examinées séparément. La mission doit être décrite avec ses lieux, dates et conditions. Si la situation réelle change, vérifiez les conséquences au lieu de réutiliser automatiquement une attestation obtenue pour un autre contexte.

Connecting concepts

Terms to know as well

Continue with the concepts, contacts and procedures related to this topic.

Multiple activityPursuit of several professional activities, particularly in several countries for the assessment of social security.Joint Social Security Centre (CCSS)The Joint Social Security Centre (CCSS) notably manages registrations and the collection of social security contributions within its remit.Labour and Mines Inspectorate (ITM)The Labour and Mines Inspectorate (ITM) is involved, in particular, in monitoring labour law and occupational health and safety.Tax residenceTax residence determines the tax connection of an individual or a company under national rules and, where applicable, a treaty.Permanent establishmentA permanent establishment is a concept linking an activity to a territory, assessed under the relevant tax framework.Tax withholding certificateThe tax withholding certificate provides the information to be used to calculate withholdings on the relevant remuneration in Luxembourg.

Put it into practice

Explore further with our guides

Practical guideCross-border entrepreneur: changing fiduciary services without disrupting continuityPractical guideCross-border teleworking: separating tax and social security rulesPractical guideSelf-employed activity in several countries: preparing the affiliation assessment

Sources and verification

References consulted on 20 September 2026. Official procedures specify the applicable conditions and exceptions.

This guide explains a general process. The applicable rules depend on your situation; it does not constitute personalised advice. Report a correction.

A definition gives you a reference point. To examine your situation, clarify your question with a professional.