Yes, that's how it works, for the trains that require a reservation.

No, because Interrail cannot book RENFE reservations anymore after RENFE made that difficult about 2 years ago. The price also depends on the type of train. Usually €4, €6.50 or €10 in 2nd class, check this page.

Booking reservations for Spanish domestic trains is not possible online. You can buy these reservations:

• at a Spanish ticket office
• possibly at Lisboa Santa Apólonia (they're reported to have a Spanish system there)
• at a Deutsche Bahn ticket office. You need to provide the train number.
• via Deutsche Bahn by phone (+49 30 2970). Collect at a DB ticket machine or receive via post (€5.90 per order). You need to provide the train number.
• Via a Swiss ticket office or by phone (scroll down to Switzerland):
  https://www.interrail.eu/en/plan-your-trip/reservations/how-do-i-book-my-reservations
• Via RENFE by phone, with limitations, see this page (scroll down to Spain):
  https://www.interrail.eu/en/plan-your-trip/reservations/how-do-i-book-my-reservations

The good thing is that domestic Spanish pass reservation are not quota-controlled, so you can book seats until the train is full.
Train numbers can be looked up via www.raileurope.com, but obviously not too long in advance, since RENFE don't publish their timetables a long time in advance.

The expensive TGVs between France and Spain can be booked:

• Via Interrail.eu (2€ booking fee per person and train + 9€ postage fee per order: delivery via post).
• Via French railways ticket office or by phone (press #85 for English, no booking fee, delivery via e-mail):
  https://www.sncf.com/en/customer-service/contact-us/telephone
• Via Deutsche Bahn ticket office or by phone (+49 30 2970, no booking fee, delivery via DB ticket machine or by post for €5.90)
• Via a Swiss ticket office or by phone (scroll down to Switzerland):
  https://www.interrail.eu/en/plan-your-trip/reservations/how-do-i-book-my-reservations
• via RENFE ticket office or by phone, with limitations, see this page (scroll down to Spain):
  https://www.interrail.eu/en/plan-your-trip/reservations/how-do-i-book-my-reservations

Thanks vey much for your detailed answer!

I had seen another post on these forums, which said that reservation fees for AVE trains could be up to E40! I’m glad that’s not true…. Great to hear also that there are no Interrail quotas in Spain!

So if I want to take a trip in Spain which has a connection, I have to either (a) make sure there is at least an hour between connections for me to run to the ticket office on the connecting station, or (b) book on the RENFE telephone line…. Can you clarify whether if I book on the phone, I can collect the reservations at *any* station… so I could collect the reservations for *both* ‘legs’ of the journey, at the *first* station… and then I could allow myself shorter connection times??

Thanks again.

You don't have to book a reservation at the departure station of the train. You can book any Spanish reservation at any Spanish ticket office that can book reservations. You could e.g. book all your reservations at the first station in Spain.

I haven't used this telephone service yet, but since you get a reference code (PNR), you should be able to get all your reservations at any station. They will just enter your code in the central system and print your reservations. There's certainly no need to allow time during changes to buy or collect a new reservation.

Yes that all sounds logical - thanks again!

The Spanish railway booking (and timetable) system, and RENFE website are shockingly complicated, inefficient, inaccurate, and user-unfriendly, considering it’s the 2020s…. I bet it was easier in the 1920s!

AVE-domestic is 10+some tiny fee for handling, but its WAY more for OVERThe border=to France (as there is no other country they run to). Then it can be well over 30. MD is 6€.

MD is 4€.