How far in advance to buy train and museum tickets

Annecy to Paris definately needs reserving as soon as possible. As you say mid August is a very busy tourist time and these trains are compulsory reservation and airline style variable pricing.

Chamonix to Annecy is less urgent, I'm not even sure whether you can reserve at all!

Thank you. Yikes!

Do you know who it would be best to book with? Haven't looked into this at all yet

The train company in FRANCE is SNCF. Look for tickets at: https://www.sncf-connect.com/en-en/home/search/od

For the Louvre, book only thru the official Louvre website ticketing function. I just looked and tickets are open thru the end of September. If you already know the day I'd go ahead and book so you get the choice of time that works for you.

https://ticket.louvre.fr/en/billetterie/3313

BTW, IF there is something you particularly want to see, look at this website first to see what days of the week certain galleries are closed.

https://www.louvre.fr/en/visit/list-of-available-galleries

Musée d'Orsay: Here is the link to their official ticketing website. Their tickets are open to Sept 13 so you can go ahead and book or you can wait a little on this one.

https://billetterie.musee-orsay.fr/billets-d-entree-au-musee-d-orsay-expo-css5-museeorsay-lgen-pg1-rg28911.html

For both the Louvre and Orsay, in mid-August it's likely to be hot. Neither museum is particularly well air conditioned. For the Louvre the worst heat will be under the pyramid so it will behoove you to move quickly thru there. In any event, if you are the kind of travelers who can get up and going to be somewhere by 9 or 930, I'd go for the earliest entries for each of those museums so you can get out by the time heat builds in the middle of the afternoon!

For Monet's house and Garden, I'd wait a bit on booking that. There are some times where there are train works and just today someone on the forum has deferred their visit because the direct train lines will be shut over the Fete Nationale in July.

https://claudemonetgiverny.fr/en/useful-information/

There are so many fraudulent ticket websites. Most of the official ones have warnings about fraudulent sites. Whatever you do, don't just google "Louvre tickets" because the first hits are probably the 3rd party or fraudulent sites.

Thank you all so much! This is really helpful!

Re: just showing up and getting a ticket for the next train going out can be done, obviously. It depends where specifically and how popular your destination is if that method is going to work.

I do that most of the time doing day trips from Paris in July. I get the ticket the night before or 2 nights before or literally the next train the following morning . Going from Paris to northern France on last minute tickets (figuratively or literally) usually works. Where I found it did not work a few times was on week-ends going to Normandie.

Thank you for the additional information Fred! That's what I usually do but as others in this thread seem to feel it's necessary to buy in advance during the busy summer season, I am going to aim for that.

And Pam, thank you so much for providing the links to buy tickets and the warning about bogus websites!