Do all trains require seat reservations?

Railway seat reservations are not always necessary on all trains. Seat reservations are not possible on most regional trains, and you can occupy any vacant seat in the carriage of the class of service as per your ticket. Though for other train types, the seat reservations maybe compulsory or sometimes optional.

Compulsory seat reservations

Seats are allocated automatically when booking your train ticket. You will also be able to change your seat according to your preferences (aisle seats, windows seats…) and subject to availability. You can request the type of seat you would prefer.

Optional seat reservations

You won’t be able to reserve a seat on regional trains. However, you can still reserve your seats with few carriers as German rail operator, Deutsche Bahn, Austrian rail operator and ÖBB. For these trains, seats reservation can be added for an extra fee by going through the Ticket page.

All first class tickets are automatically assigned a seat reservation, which is included in the ticket price.

Trains without seat reservations

Lots of regional trains do not have seat reservations at all. Most regional trains typically have plenty of spare seating for all passengers, though you may find that they are busy during peak commuter travel times (when people travel to work in the early morning and return in the evening).

"Unreserved seating" mentioned on the confirmation?

If your booking confirmation says "unreserved seating" against  a particular train, it means that the seat hasn't been added for the particular train. You may need to book the seat reservation separately, depending upon whether the seat reservations are compulsory or not.