I am flying from USA to Vienna with the flight having a scheduled stop in Frankfurt. Do I have to go through customs in Frankfurt or Vienna? Which airport will l I have to take my luggage through customs?
Thanks from an inexperienced traveler.

>>Do I have to go through customs in Frankfurt or Vienna<<

You will go through Immigration (Passport control) at Frankfurt. Customs is about luggage - assuming both flights are on the same ticket, you will not see your bags or go through Customs until Vienna.

Your flights no not necessarily need to be on the same ticket. If your bags are checked through to Vienna then that's where you'll get them and go through customs.

>>Your flights no not necessarily need to be on the same ticket. If your bags are checked through to Vienna then that's where you'll get them and go through customs.<<

It may not be 'necessarily so' but with separate bookings it is much more common that bags are not interlined.

I'm assuming that is not a problem for the OP though, since he posts "the flight having a scheduled stop . . ." which sounds like he is talking about a single booking.

Sounds like just a connecting flight on one ticket

When I flew to Lithuania via a stop in Frankfurt, it was immigration in Frankfurt. I didn't see my luggage until Lithuania. I believe this is how all my other connecting flights into Europe from the US worked.

YOu can ask the gate agents at check-in questions like this.

I'd imagine it's a UAL/LUF ticket with a connection in FRA, and that you wouldn't have to get your bags.