No one knows for certain how long people have lived in what is now Cambodia, as studies of its prehistory are undeveloped. 

A carbon-l4 dating from a cave in northwestern Cambodia suggests that people using stone tools lived in the cave as early as 4000 bc, and rice has been grown on Cambodian soil since well before the 1st century ad. The first Cambodians likely arrived long before either of these dates. They probably migrated from the north, although nothing is known about their language or their way of life.