The 'Palaeolithic' period is the term for the Old Stone Age, the immensely long period of hunter-gatherers extending from the time when humans first evolved up to about 10,000 BC. In Britain, the earliest evidence of human activity dates from about 450,000 years ago, although there are long periods (of 100,000 years or more) when there appears to have been no human presence. The advance and retreat of the glaciers in the Ice Ages saw different extremes of climate in Britain, from tropical in the inter-glacial periods to barren permafrost during the coldest eras.

The period has been divided up by archaeologists into the Lower (the oldest), Middle and Upper Palaeolithic to indicate when social and technological developments – mainly increasingly sophisticated flint tools – occurred. Neanderthal Man was supplanted by Homo sapiens, modern man, during this epoch, and what are popularly thought of as 'cavemen' also belong to this period. Their remains have been found in caves, such as those at Cheddar (Somerset), but they probably lived more often in open country, moving around as hunters and gatherers in pursuit of their sources of food.

Mesolithic