An A1 certificate is a form used to confirm the country in which an employee or visitor currently pays for their social security contributions. If an individual will be travelling for work, as a posted worker or for business visits in another EU member state, they will be required to have an A1 certificate before they travel.
Within EU policy, an individual can only be subject to one country’s social security at a time. A1 certificates are typically considered when an individual is travelling to work or visiting for business and will therefore be subject to social security contributions in their host country as well as their home country.