Reservation fees are not included in the Pass. We recommend booking any necessary seat reservations in advance, especially on busy routes. If you wait to book your reservations, you may discover that no seats are available to book during your preferred travel times.
You can travel without a seat reservation on most regional trains, but buying a seat reservation is mandatory for some high-speed, international, and night trains.
Check out the full list of railway companies covered on the Interrail website.