Travelling from Chiang Mai to Laos can be easy because Laos is a neighbouring country to Thailand. The fastest way to get there is by plane and you can fly direct from Chiang Mai to Luang Prabang daily. There are no direct flights to the capital Vientiane but you can either fly via Bangkok or direct to Udon Thani and then transfer by bus across the border. From the airport at Udon Thani there is a bus waiting to take travellers to the border and there are good value taxis to take you from the border to the city. Check the border requirements for passports before going as sometimes they don't allow certain nationalities to cross.
The most common (and the cheapest) way travellers enter Laos is by bus. There are both mini vans and larger, slower buses going from Chiang Mai to Vientiane. Almost all of the buses run overnight, most leaving at 19:00 from Chiang Mai and arriving at the border at 6:00 or 7:00 the next morning. Depending on the company the total journey can take between 14 -18 hours and costs around 1,000 Baht. You can book the minivans or buses at most guest houses or at the Arcade bus station.
The most unique way to get to Laos is by boat. This involves first taking a bus to Chiang Khong (Thailand), crossing the border there into Huay Xai (Laos) and then catching either the slow boat or the fast speed boat to Luang Prabang. The slow boat is cheaper and more popular but takes two days, and an overnight stop, to get to Luang Prabang. The boat is basic and sells only water, beer and instant noodles. The fast boat is uncomfortable with a loud engine but takes only 6 hours to arrive in Luang Prabang. Most travel agencies in Chiang Mai can organize the entire trip to Luang Prabang as a package. It is possible to do the journey independently but the price ends up about the same.