Missed connecting flight because of a delay, who is responsible?

This is where many travelers get confused. It depends on your booking:

• One booking (single ticket): if the first flight was late, the airline normally rebooks you on the next flight at no extra cost. For long waits, they may also provide meals or a hotel.
• Separate tickets: the second airline usually isn’t responsible. Contact them immediately and ask if they can change your flight.

Don’t forget to keep your boarding passes, receipts, and the time of every chat or call with the airline.

I found this missed connecting flight help page useful for understanding who pays for what.