Just Arrived gives you all the keys to declare your place of residence in Luxembourg !
When you move in Luxembourg more than six months out of twelve, it is mandatory to declare your place of residence at the population office of your communal administration. You can make this statement yourself, or leave this task to your spouse/partner with whom you live. If necessary, a guardian, a curator, a legal administrator, an ad hoc administrator or a special agent can also declare your residence on your behalf, based on a valid identity document and a title allowing them to act accordingly. However, you need to hurry when undertaking these steps because your statement of residence must be made within 8 days of your arrival. The period is also more shortened for third country nationals since they are required to report their arrival on the territory within 3 days after their arrival.
To declare your place of residence in Luxembourg, an identity card or a passport will be required. Guichet.lu also indicates that the “persons who are nationals of third countries must also submit, if need be, an entry visa or a residence permit established by another State member of the European Union and assimilated. More info here.
If you leave your home to move elsewhere in the Luxembourgian territory, it is also important to tell your new communal administration so that it deletes you from the registry of your former place of residence. It is also the case if you leave the territory to go and live abroad. More info here.