If you are thinking of coming to Courmayeur / Aosta Valley by plane you have several options:-
Flying into Italy
The closest airport to Courmayeur - Aosta Valley is in Turin - Caselle Aeroporto di Torino (Turin Airport) (distance: 150km) otherwise you have the International Airport of Cuneo in the same area (distance: 240km).
You can also fly to the international airport of Milan - Milan Malpensa Airport (disance: 215 km) or Milano Linate Airport, this one is a little bit further (distance: 235 km). Another option is in Bergamo Orio al Serio International Airport (distance: 260km)
Flying into Switzerland - most convenient way!
Geneva Airport, in Geneva, Switzerland are two of the most convenient airports for getting to Courmayeur. Geneva Airport is closer to Courmayeur (distance: 112km) via the Mont Blanc Tunnel passing Chamonix Mont Blanc.
Flying into France
Another way to get to Courmayeur which is closer than some of the Italian airports is Lyon-Saint Exupéry Airport (distance: 206km)