The international airports at Vientiane and Luang Prabang are served by national carrier Lao Airlines www.laoairlines.com and a few others, including Thai Airways www.thaiair.com, Bangkok Airways www.bangkokair.com (Luang Prabang only) and Vietnam Airlines www.vietnamairlines.com. Some seats on flights of Vietnam Airlines are reserved for Lao Airlines (codesharing / better price). Pakse is the third international airport, with flights to/from Siem Reap (Vientiane - Pakse - Siem Reap by Lao Airlines) and from/to Hochiminh city.
Laos used to be off-limits to low-cost carriers, however AirAsia www.airasia.com now flies to Vientiane from Kuala Lumpur three times a week. Another cheap option for getting to Vientiane is to fly to Udon Thani in Thailand with discount airlines Nok Air or Air Asia and connect to Nong Khai and the Friendship Bridge via shuttle service directly from the airport (40 minutes); from here Vientiane is just 17 km away.