Notre Dame paris

You can try by logging in a couple of days in advance. I could not secure the tickets so went ahead on a Sunday early evening, stood in a long line for 20 minutes and was in. I sat for part of Mass and then worked my way around the church. It was very hard to get around with all the people and another Mass starting. But it is beautiful and well worth the visit.

If you put "Notre Dame tickets" in the search bar above you can find all the information you need, Filter "forum" and 6 months or less.

rosemary,
I see you asked about this before. The answers given then still apply.

This is the official website: https://www.notredamedeparis.fr/en/

You still do not need tickets. That was for the initial opening. If you want to avoid long lines, go early in the day and avoid weekends and holidays.