If you give the details  (departure date, time and route) it will be easier to give advice.

The details are:

August 7th : From Milan to Genoa , Departure time 07:38

August 8th : From Genoa to Monaco, Departure time 07:19

There might be more routes involved later but my questions stand regarding the interrail system in general. Do I have to look into each train separately?

There might be different rules in different countries if the train get full, so if you can say what countries you plan to visit.

I will be visiting Italy and France. Other routes involve Nice, Cannes and Marseille but the dates are not certain yet so I cannot provide any more info unfortunately.

Milan - Genoa: That is an IC train, in Italy these require reservations, cost €3

Genoa - Monaco: Both these are regional trains R, IR,(TER in France) these in most cases do not require or even allow reservations.

You should refer to the pages on Eurail.com and “Rail Network guides” section in app to explain which trains in which countries are valid and need reservations.

To get reservations read this thread:

I will look into it, thanks a lot!

@Angelo @rvdborgt @Hektor Are there any recommendations regarding making reservation on trains with no mandatory reservation in Italy and France? Or are the trains in France and Italy either with mandatory reservation or with no reservation possible?

I know that in Germany and Austria people without reservations might have to leave the train for security reasons if the train gets too crowded. In those countries it might be wise to make a reservation now during the summer even if reservation is optional.

In Italy the only train with optional reservation are the EC trains Munich-Innsbruck-Verona-..., RJ Venice-Vienna (both need 10€ fee to use them in Italy, but reservation optional. Via DB and Trenitalia Ticket office the reservation is for free) and also the EC Vienna-Ljubljana-Trieste. Reservation optional and fee is abou 3€.

@anna and others: in IT and in FR even more its quite simple: either a train MUST be REServed (this refers to the faster/long distance/ICtrains, in FR the TGV and IC) OR it cannot be done. The planner of bahn.com has the best and reliable info for that. The same applies to ESpana-except that the NON-RES trains there are limited to the cercanias around big towns.

DE/germany and AT/Austria are a kind of special cases and this phenomenon of clearing trains of standees does not happen that often-and if it does, mostly for special hi-speed sections. In DE then very often money/vouchers are offered.

There are still a few IC trains in France with optional reservations. In Italy, AFAIK IC also has optional reservations but for longer distances it's a good idea to book since it is not indicated if seats have bene booked. Some ECs from/to Italy also have optional reservations, as Angelo wrote.