Flights from USA & CANADA to Paris:

The Loire Valley is easily accessible from all the Paris airports due to the excellent rail and road networks.

For all flight information and more, visit the website for both Paris Roissy Charles de Gaulle and Paris Orly Airports:

http://www.aeroportsdeparis.fr/Adp/en-GB/Passagers/

From London Heathrow, Air France and British Airways fly frequently (up to 17flights daily) to Paris; the trip takes 1 hour. 

You can reach Paris from most other major European capitals. The best option is to fly on France's national airline, Air France, which has more connections into Paris from European capitals than any other airline.  

Although only serviced by budget airlines from London Stansted  Tours airport is a good option as a destination as it gives excellent access to the whole of  Loire Valley/Centre region. The airport itself is a 10 minute bus/taxi trip to the city centre where you have access to the  TGV and SNCF rail networks.