The Notre-Dame Cathedral in Paris is open to all, freely and at no charge, regardless of the reason for your visit.
Access to Masses is without reservation, via the dedicated queue for services, which opens 20-30 minutes beforehand, opposite the Last Judgement portal.
Find the service and Mass timetable to plan your visit to the cathedral.
The veneration of the Crown of Thorns, is also open to all. As with Masses and services, there is no need to book: a dedicated queue opens 20 minutes before the celebration, via the entrance opposite the Last Judgement portal.
The chairs in the nave are reserved for those wishing to attend these services.