The hilltribes of northern Thailand have been called fourth world people, due to the fact that they are migrants who continue to migrate and pay no regard for national boundaries. They are spread over Thailand, Laos, China and Burma. Around Chiang Mai these people have villages in the mountainous jungle which can be visited on treks. You must choose carefully if you wish to do this as it is not a human zoo but a real life village. But if you do, and decide to stay overnight, the experience, despite the hardship, can be unforgettable.
Each hilltribe has different customs, costumes and language.The most popular, the Karen, originally migrated from China and occupy the mountains west of Chiang Mai to Mae Hong Son. But others such as the Hmong were forced out from Laos after they sided with the Americans in the Vietnam war. And the Lahu have escaped Burma were their relatives are still persecuted by the repressive regimes there. Each has found the 'slash 'n burn' policy hard and in the past has fallen back on heroin production. The authorities have tried to wean them off this by introducing tourism aka trekking. But there are still poppy fields in jungle clearings watched over by armed guards.
The only way to visit them is with a trek. Choose the trek which suits your budget and fitness level. If you don't want to do any ardous walking then there are treks in which you are taken by car to villages near Chiang Mai. But for the big treks you will be taken twenty miles west into the mountains and made to walk from there. There is alot of 'Lonely Planet' snobbery about undiscovered villages but you will bump into other trekking parties on the trails - it's a fact - as trekking is big business and the trails nearest to Chiang Mai are used by alot of groups.
Shop around for your trek. Also chose wisely abou the length of trek. The 5-7 day treks can be agonisingly exhausting and we saw one come back to the Daret Guesthouse where the trekkers looked half-dead. You must also remember that this is not a luxury expedition it is likely that you will not shower or sleep in a bed for the nights you want to be away. A good trekkng company will charge 500-600 baht a day which should include rafting and elephant riding. You guide should be knowledgeable and make sure he has a good grasp of english as he is in your trust for a number of days. He is responsible for your welfare and should cook for you. Take as little as possible - you will probably only need - insect repellant, spare shorts, shirt, cold water, toiletries and sturdy boots. Be prepared for the adventure of a lifetime.