For some routes, an additional seat reservation is required. Seat reservations are not included in your Eurail or Interrail Pass, but for a fee they guarantee you a comfy seat on busy routes across Europe. On most high-speed trains and all night trains, seat reservations are mandatory.
For a fun set of instructions, check out our Instagram highlight, here.
Another option is to book seat reservations directly with the rail carrier. Our community put together this handy guide on how to do that, here. Feel free to ask questions, but please be sure to start a new topic first.