The shape of contemporary Cambodia has come about through a classic historical squeeze. As the Vietnamese pushed southward into the Mekong Delta and the Thais pushed westward towards Angkor, Cambodia shrank. Ironically it was only the arrival of the French that prevented Cambodia going the way of the Chams, a people without a state, and it that sense it was a protectorate that protected.

Cambodia today is 181,035 sq km in size, making it a little over half the size of Vietnam or about the same as England and Wales without Scotland. The country is wider (about 580km east-west) than it is tall (about 450km north-south); to the west it borders Thailand, to the north Thailand and Laos, to the east Vietnam and to the south the Gull of Thailand.

Cambodia's two dominant features are the mighty Mekong River, which is, incredibly, 5km wide in places, and the vast Tonle Sap Lake - see the boxed text on below for more on this natural miracle. Many visitors take express boats up and down the Mekong, linking towns like Kom-pong Cham and Kratie. The Mekong, which rises in Tibet, flows almost 500km through Cambodia before continuing, via southern Vietnam, to the South China Sea. At Phnom Penh it splits into the Upper River (called simply the Mekong or, in Vietnamese, the Tien Giang) and the Lower River (Tonle Bassac, or the Hau Giang in Vietnamese). The rich sediment deposited during the Mekong's annual wet-season flooding has made for very fertile agricultural land in the centre of Cambodia. This low-lying alluvial plain is where the vast majority of Cambodians live, fishing and farming in time with the rural rhythms of the monsoon.

In the southwest, much of the landmass between the Gulf of Thailand and the Tonte Sap Lake is covered by a mountainous region formed by two distinct ranges: the Chuor Phnom Kravanh (Cardamom Mountains) in southwestern Battambang Province and Pursat Province, and the Chuor Phnom Damrei (Elephant Mountains) in the provinces of Kompong Speu, Koh Kong and Kampot.

South of these mountains is Cambodia's lengthy coastline, a big draw for visitors on the lookout for isolated tropical beaches. There are islands aplenty off the coast of Sihanoukville, Kep and Koh Kong, all of which offer promising potential in the years to come.

Along Cambodia's northern border with Thailand, the plains collide with a striking sandstone escarpment more than 300km long and 180m to 550m in height that marks the southern limit of the Chuor Phnom Dangkrek (Dangkrek Mountains). Most visitors only see these moun­tains if making the overland pilgrimage to Prasat Preah Vihear. In the northeastern corner of the country, the plains give way to the Eastern Highlands, a remote region of densely forested mountains and high plateaus that extends eastward into Vietnam's central highlands and northward into Laos. The wild provinces of Ratanakiri and Mondulkiri provide a home to many minority peoples and are taking off as traveller hotspots in Cambodia.