By ship
Boats ply the Mekong to and from Huay Xai at the Thai border, stopping in Pakbeng where you can catch overland connections towards the northeast and the border with China. The trip takes 2 days both days about 9 hours by slow boat, or 6 bone-rattling hours by speedboat. There are also operators now offering 2-day "luxury" cruises.
Expect to spend the night in Pakbeng if you're taking a slow boat the safest option, or to arrive in Luang Prabang deaf, shaken and either exhausted or exhilarated from six hours in a speedboat. There is also a twice-weekly "one day comfortable boat" between Luang Prabang and Huay Xai, but the cost is significantly higher.
Slow boats leave every day, the last one at 11AM. The trip from Luang Prabang to Huay Xai costs at least 250,000 kip January 2012, the trip to Luang Prabang from Huay Xai costs 900 baht Sep 2011. The slow boat leaves Luang Prabang at about 8.30, from the middle of the town, and arrive around 18.00 at Pak beng.
In Huay Xai it's best to take a quick tuktuk from the border crossing to the boat landing or about 15min walk and purchase your tickets at the boat landing because all the tour agencies in town charge a commission, and agents usually don't have reliable information about the quality of the boats. It is common to have to switch to a different boat in Pakbeng, so you may end up in a boat of higher or lower quality for the second half of the journey. The two day boats have nice comfortable car seats and it is no longer necessary to purchase any cushions.
The slow-boat is generally packed - so much so that there may not enough seats to go round. Arriving early will mean a longer day, but most likely a better seat, towards the front and away from the engine.
The slow boat trip proceeds in a pleasant 20-30km/h and offers nice views to the nature and village life on the banks of the Mekong river. Most of the passengers are foreign tourists. Occasional locals take the boat only for short hops between the river side villages, but prefer to take the bus for the full distance from Huay Xai to Luang Prabang. So you won't be able to observe any local boat travellers, as the boat ride offers just the usual sight of tourists drinking Beerlao.
If you choose to travel on the speedboat a light canoe with a very powerful engine, a crash helmet and life-jacket should be provided - it is not recommended to travel in a speedboat without this essential safety equipment. It is also recommended that you make your bags as waterproof/water-resistant as possible and wear a rainjacket - the boat can generate quite a bit of spray, plus any showers you might encounter along the way will sting like needles against any exposed skin. On sunny days, sunscreen is invaluable as there is no roof/shade on these speed machines. The journey to Huay Xai can be reduced to as few as 4 hours in the wet season, with a lunch stop at Pakbeng. However, some consider this means of transportation less safe, especially in the dry season. Earplugs are strongly recommended. Travellers who are concerned about creating as little environmental impact as possible may want avoid speedboats, as they are heavier polluters than the slower options. Travel agents in LP will sell the tickets for 320-370,000 Kip, you will need a minivan to take you the 10km north to the fast boat pier.
The third option is to take a "luxury" cruise. The major operators are Luang Say (http://www.luangsay.com) and Nagi of Mekong (http://nagiofmekong.com/). As of 2009, both operate two-day cruises to Hauy Xai that stop in Pak Beng for the night. Since October 2011 a third player has entered the market, Shompoo Cruise. Although the journey takes as long as taking the slow boat, these operators offer vastly superior facilities and equipment than public slow boats, and you should be prepared to pay a premium for it. Tickets for all three operators can be bought at most travel agents in town.
As per November 2011 the prices are approx. 220K for a slowboat, 280K for a speedboat. 3'000K for Luang Say, 1'200K for Nagi of Mekonand both including a night in a hotel and 640K for Shompoo. Some travelers are reporting that prices of Luang Say and Nagi of Mekong can be bargained down.
There is no public boat service to Vientiane, but it may be possible to do the trip by private tourist boat when the water levels are high enough. Read more about fast and slow boats in the Laos country guide.
