The Eurail Pass does include travel on most high-speed trains across Europe, such as the TGV in France, the AVE in Spain, the Frecciarossa in Italy, and the Eurostar connecting London to the continent. However, there is a major "catch" that many first-time travelers overlook: the mandatory seat reservation fee. While your Eurail Pass covers the basic "fare," high-speed and international "premier" trains require a confirmed seat reservation that can cost anywhere from €10 to €30 per person, per journey. These reservations are limited and can sell out weeks in advance, especially during the summer. In contrast, slower regional trains generally do not require reservations, allowing you to simply hop on and off with just your pass. To maximize value, many savvy travelers use the "Eurail Rail Planner" app to filter for trains that don't require reservations, or they budget extra for the convenience and speed of the 300 km/h lines. It’s also worth noting that the Eurostar is particularly popular and requires booking your pass-holder seat well in advance to avoid being shut out of a specific departure time.