By plane
There are currently no direct international flights into or out of anywhere in Idaho. If you're coming in from overseas, rest assured you'll go through United States customs before boarding a flight to an Idaho location.
By far the largest airport in the state, Boise Airport IATA: BOI ICAO: KBOI is the main airport in southern Idaho. Flights to and from Boise are available from most major cities in the western United States, as well as Minneapolis and Chicago. Boise Airport also offers a good selection of charter flight services.
Northern Idaho is primarily served by Spokane International Airport IATA: GEG ICAO: KGEG, located in eastern Washington approximately 20 miles 32 km from the Idaho border. The non-stop schedule to and from Spokane is similar to Boise. Despite the airport's name, there are currently no scheduled direct international flights to Spokane.
Other Idaho airports include Idaho Falls Regional Airport IATA: IDA ICAO: KIDA in eastern Idaho, and the seasonal, tourist-based Friedman Memorial Airport IATA: SUN ICAO: KSUN near Sun Valley. Idaho Falls is a good flight destination for nearby Yellowstone National Park.
Smaller airports, such as in Lewiston LWS, Twin Falls TWF and Pocatello PIH offer only a limited commercial flight schedule. In the case of the latter two, the only commercial flights available are to and from Salt Lake City.
Airlines serving Boise include Delta, Frontier, Horizon, Southwest, United and US Airways. Spokane is served by the same carriers, as well as by Alaska Airlines.
SkyWest Airlines serves several Idaho cities from its Salt Lake City hub, including Boise, Lewiston, Idaho Falls, Twin Falls and Pocatello.
United Airlines sub contracts SkyWest Airlines for its San Francisco to Boise flights. Don't be surprised if you board a plane marked in SkyWest colors. Your baggage ends up in the same place.
By train
The lone city in Idaho with rail passenger service is in the panhandle at Sandpoint. Amtrak's "Empire Builder" stops in Sandpoint in the middle of the night just before midnight westbound, about 230 AM eastbound on its daily runs between Chicago, Milwaukee, St. Paul/Minneapolis, Glacier National Park, Spokane, and Portland/Seattle.
By car
You could also drive to North Idaho from Seattle or more easily from Spokane.