Whether or not you require a seat reservation is dependent on the kind of train you'd like to travel on. As a rule of thumb, most high-speed, international, and overnight trains require an additional seat reservation, while regional trains and trains in specific countries do not.
When a seat reservation is mandatory, it will be clearly labelled on our website as well as on the Rail Planner app. On journeys with mandatory reservations, you'll see a text saying: "Seat reservations required."
When a seat reservation is required, we highly recommend booking your seats as soon as possible.
If a particular train does not require seat reservations, the website and the Rail Planner app will state that no reservations are required.
It is still possible to make reservations even though they are not mandatory. This can sometimes be useful to guarantee your seat on a busy train. You can find more information on how to do that here.
If you have any further questions, please feel free to reach out to our customer service team.