Lufthansa flight from US - IAD to LJU with a 2 hour layover in Frankfurt

Are both your flights on one ticket?

You will have to go through passport control in Frankfurt, getting your passport stamped for Schengen entry. 2 hours should be adequate. If you did check luggage, it would not be a problem since it will be on the baggage claim belt in Ljubljana where you go through customs, which is nothing more than exiting through the "Nothing to Declare" door.

Two hours seems tight but possible with Frankfurt. I just transited through coming home from the holidays. It's a huge airport. Heading back, my husband's flight to Frankfurt was delayed and he had two hours. He made it but had no extra time.

Carry on vs checked won't make a huge difference, as they'll check your bags all the way through. It's just the US that makes you pick up your bag.

It’s an adequate layover and I would not worry about it. Though, as others have said, Frankfort airport is huge, and you should keep an eye on the clock.

Thank you everyone! I've gained some peace of mind and feel like I can make an educated decision now!