Yes, you can use a Eurail Pass on TGV (Train à Grande Vitesse) high-speed trains in France, but it is not a "hop-on, hop-off" system. TGV trains require a mandatory seat reservation, which is not included in the price of your Eurail pass. In 2026, these reservations typically cost around $10 to $20 for domestic routes within France if booked in advance, but can rise significantly for international TGV Lyria (Switzerland) or Eurostar (London/Belgium) routes. Because the number of seats allocated to pass holders is limited, popular routes can sell out weeks in advance during the summer or holidays. You can book these reservations through the Eurail "Rail Planner" app, the SNCF website, or at a French train station ticket office. If you board a TGV without a valid reservation, you may be treated as a passenger without a ticket and face a heavy fine, even if you have an active Eurail day on your pass. For a budget-friendly alternative, consider taking TER (Regional) trains; they are slower and require transfers, but they do not require reservations or extra fees for Eurail holders.