Most nonstop flights between North America and Italy serve Rome's Aeroporto Internazionale Leonardo da Vinci (FCO), better known as Fiumicino, and Milan's Aeroporto Malpensa (MXP), though the airports in Venice, Pisa, and Naples also accommodate nonstop flights from the United States. Flying time to Milan or Rome is approximately 8–8½ hours from New York, 10–11 hours from Chicago, and 11½ hours from Los Angeles.
Alitalia has direct flights from London to Milan and Rome, while British Airways and smaller budget carriers provide services between Great Britain and other locations in Italy. EasyJet connects London’s Gatwick and Stansted airports with 19 Italian destinations. Ryanair flies from Stansted to 29 airports. Since tickets are frequently sold at discounted prices, investigate the cost of flights within Italy (even one-way) as an alternative to train travel.
You can take the Ferrovie dello Stato Italiane (FS) airport train or bus to Rome's Termini station or to Cadorna or Centrale in Milan; from the latter you can then catch a train to any other location in Italy. It will take about 40 minutes to get from Fiumicino to Roma Termini, less than an hour to Milano Centrale.
A helpful website for information (location, phone numbers, local transportation, etc.) about all of the airports in Italy is www.italianairportguide.com.