Social security and taxes
The EU wants to ensure that you are part of a social security system and that you do not lose your rights, regardless of the member state you decide to work in.
You are insured for social security purposes in the country you work in. You are entitled to the same social security benefits as nationals of the country in which you work. These rights cover sickness and maternity benefits, disability, old-age and widow's/widower's benefits, benefits payable for accidents at work, occupational illness, death and unemployment, as well as family allowances. You will be required to pay the same level of contributions as host country nationals.
You cannot be excluded from benefits on grounds of nationality, for reasons of residence, or for any other discriminatory reason.
By working in another member state and by transferring your residence there, you will become "resident for tax purposes" there. The definition of fiscal residence varies from one member state to another. You must comply with the laws of the country where you have established your residence.
If you are fiscally resident in a country, you must declare all your income ("worldwide" income). You may also be subject to other taxes such as wealth tax or inheritance tax.
Tax agreements have been concluded between the member states of the EU, which are intended to avoid double taxation, if you derive income from different countries.