Notre Dame de Paris - tour guide recommendations?

holmmary, No paid guided tours are allowed inside Notre Dame. There are free tours given by volunteers, called CASA, which are offered some afternoons. Inside, explanations are given using headphones. You can use the audio guide headphones on a self-guided tour or with CASA. There are occasionally certified, prearranged, guided tours allowed, not often, but once again, headphones are required so that any speaking is quiet and soft, so as to be deferential to the sacred space. There can be no commentary from a guide without headsets. You can go to the official website for more details: notredamedeparis.fr/en/
They warn about scammers who try to sell you a ticket for the cathedral. Entrance is always free. No third parties are allowed to sell access or entry. It is a church and no one has to pay to visit the church. Make reservations only on the official website. A possible expense would be renting the audio guide set. Or you can download the mobile app for free. (You will need headphones to avoid having your phone speaker on.) There is also a fee to visit the Treasury, 12 euros. The website is very easy to use.

Enjoy your time there.

I suggest Paris Walks and their Île de la Cité walk. They don't take you into Notre-Dame of course, but you certainly hear about it.

Thanks very much for your replies!
I had been hoping for a tour like those given by Malcolm Miller in Chartres, still after 55 years the most informative cathedral tour I've ever been on. I see that he is still (!) giving private tours there. But we're not going to Chartres.
I appreciate the recommendations for the walks.

Here is the link to the free visits run by CASA volunteers in English. I did one last Fall and it was very good. They provide whisper sets and take you thru. Mine did a quick rundown of the facade of the cathedral as we were standing outside.

https://www.acck.fr/GuidesCasa-calendrierCasa/

They are not nearly as intense as Malcolm Miller's tours, though!