booking high speed train from Paris to Barcelona

Kathleen, Capitan train: https://www.captaintrain.com/en
or the SNCF (French Railways) site: http://www.sncf.com/
But Captain Train is a lot easier to use and charges the same prices. I just looked Paris to Barcelona on Captain Train for Monday 10 October, and it gave me a price of €39 (per person 2nd class). Can't beat that!
The earlier you book, the cheaper the price. But, once you book, you can't change your mind.
Make sure you get "print-at-home" tickets. The ticket will have date, time, train number, coach and seat number on it. Then you will have all you need ready before you leave home.

Thanks for the site. We are looking to leave Paris on October 18th. The cost is € 79!

I used captain train for that purchase as well - it was much easier for me to pick seats on that site vs. the French rail site.

You will love this trip through Provence! Do yourself a favor and bring some food. The stuff in the dining car is meh.

No need to use the SNCF site in French; here is the English version: http://en.voyages-sncf.com/en/
It's become much easier to use and no prices will be lower. I recently bought a ticket for that train with no problems.

I always use Captain Train when booking European trains. Easy and fast to use.