North-western Cambodia is a region of Cambodia and includes the provinces of Banteay Meanchey, Oddar Meanchey, Preah Vihear, Siem Reap and the part of Stoeng Treng to the west of the Mekong.
Control of much of this area has often passed between the various regional powers. It is now part of Cambodia thanks to the French, whose sabre rattling forced the Siamese into relinquishing it (along with Battambang) in 1907. The region had been Siamese since 1867, thanks again to the French who gave it (and Battambang) to Siam in exchange for unobstructed French control over the remainder of Cambodia. Before then, a nominally independent Cambodia existed as a vassel state of Siam and Vietnam.
Much of north-western Cambodia is characterized by poverty. Siem Reap province is one of the poorest in the country, despite its valuable temples. Infrastructure construction has been booming, though only since around 2008; this makes many older reported journey times and maps hopeless outdated. Outside the towns, car batteries provide expensive electricity to village homes.
For now, development means only the blazing of asphalt trails through remote areas. The growth of businesses and expanded tourism will surely follow, so make sure to explore off the tourist trail and get a genuine insight into Cambodia's beautiful struggle.
The region is served by Siem Reap - Angkor International Airport  (IATA: REP | ICAO: VDSR) which has has frequent domestic flights from Phnom Penh and is internationally linked from the following destinations:
The following roads are all paved:
If you're only making your way between towns in the region, then the days of rough, impassable roads and adventure are over. Most main routes are now paved, with the exception of only a few.
There are a range of bus companies serving all towns large enough to be worth visiting. The larger the town, the more regular the service.
Where the bus companies don't go, one should usually be able to travel by taxi. For the best chance of success, organize your taxi the night before, otherwise an early start may be needed to secure a place in a share-taxi.
By pick-up truck
It's not as simple to organize a pick-up truck as it is a taxi, but they have a different market - budgets outside tickets. Used for passengers and cargo, pick-up trucks head everywhere, providing a broad network, linking most every lonely village. If it weren't for these banged up wagons, most of the region wouldn't have access to affordable transport. Simply stand on the edge of the road, and flag the first one down.
By kuyon (tractor)
Short trips outside towns can be made by hitching a ride on a slow, rustic, local tractor. Just flag down the first one heading your way. This is effectively hitch hiking, and comes with the usual dangers. USD$0.75 per 15km would be appropriate.
Siem Reap hosts an vast array of things to do beyond its temples. Ride horses, elephants, jeeps. Visit museums. Take cookery classes. Shoot things. Watch apsara dances. Get massaged. Take a boat on the Tonle Sap. Learn Khmer.
Outside Siem Reap the main pastime is marvelling at being in the middle of nowhere (much of Cambidia's development is focused on its south east): watch rice fields being burnt, planted, harvested. Stare at starry skies away from city light polution.
Siem Reap hosts the region's gastro-centre. All tastes and budgets are catered for. Elsewhere it's the usual provincial fare of soups, fruit, rice, meat, and veg.
Similar to the dining scene. Dry martinis can only be found in Siem Reap and the casinos near the border crossings. Every two-bit hut will serve cold water, cola and beer; local style coffee (cold and sweet) can be found just about everywhere.
North Western Cambodia is home to the K5 mine belt, a 700km long, 500m wide band of landmines that runs parallel to the Thai border. Although parts have been cleared, much remains. When travelling in remote areas, never stray off the road or track. It's just not worth the risk.
Three of Cambodia's six overland crossings with Thailand are in this region: