The Stone Age is a broad prehistoric period during which humans widely used stone for tool-making. Stone tools were made from a variety of different sorts of stone. For example, flint and chert were shaped (or chipped) for use as cutting tools and weapons, while basalt and sandstone were used for ground stone tools, such as quern-stones. Wood, bone, shell, antler (deer) and other materials were widely used, as well. During the most recent part of the period, sediments (like clay) were used to make pottery. A series of metal technology innovations characterize the later Chalcolithic (Copper Age), Bronze Age and Iron Age.

The date range of this period is ambiguous, disputed, and variable according to the region in question. While it is possible to speak of a general 'stone age' period for the whole of humanity, some groups never developed metal-smelting technology, so remained in a 'stone age' until they encountered technologically developed cultures. However, it is believed that this period began somewhere around 2.5 million years ago with the first hominid tool makers in Africa, most likely Australopithecus garhi.
Due to the prevalence of stone artifacts, which are frequently the only remains which still exist, lithic analysis is a major and specialized form of archaeological investigation for the period. This involves the measurement of the stone tools to determine their typology, function and the technology involved. This frequently involves an analysis of the lithic reduction of the raw materials, examining how the artifacts were actually made. This can also be examined through experimental archaeology, by attempting to create replica tools. This is done by flintknappers who reduce flintstone to a flint tool.

The term inexactly suggests that human advancement and time periods in prehistory are only measured by the type of tool material, rather than, for example, social organization, food sources exploited, or adaption to climate. This is a product of a time when finds of artifacts were the main goal of an archaeological excavation. Modern archaeological techniques stress a wider collection of information. Neat divisions such as the term Stone Age are increasingly limited.

Changes in past societies over the millennia were complex and involved multiple factors such as the adoption of agriculture, settlement and religion.Another problem connected with the term Stone Age is that it was created to describe the archaeological cultures of Europe, and that it is inconvenient to use it in relation to regions such as some parts of the Americas and Oceania, where farmers or hunter-gatherers used stone for tools until European colonisation began. Metal-working was a much less important part of people's lives there and it is more useful to use other terms when dividing prehistory in those areas. The same incongruence applies to the Iron Age worldwide, because in the Americas iron (but not copper, silver or gold) was unknown until around 1000 CE, in Oceania until the 17th century or the 18th century.

Near the end of the Pliocene epoch in Africa, an early ancestor of modern humans, called Homo habilis, developed the earliest stone tools. These were relatively simple tools known as choppers. Homo habilis is presumed to have mastered the Oldowan era tool case which utilized stone flakes and cores. This industry of stone tools is named after the site of Olduvai Gorge in Tanzania. These humans likely subsisted on scavenged meat and wild plants, rather than by hunting prey. Around 1.5 million years ago, a more evolved human species, Homo erectus, appeared.

This period is most well-known as being the era during which the Neanderthals lived (c. 120,000–24,000 years ago). The stone artifact technology of the Neanderthals is generally known as the Mousterian or more precisely Neandertal traits was found also in younger Chatelperronian, Aurignacian and Gravettian archeological cultures. The Neanderthals traits eventually disappeared from the archaeological record, replaced by modern humans traits which first appeared in Ethiopia around 120,000 years ago although often identified as Archaic Homo sapiens. Neanderthals nursed their elderly and practised ritual burial indicating an organised society. The earliest evidence (Mungo Man) of settlement in Australia dates to around 40,000 years ago when modern humans likely crossed from Asia by hopping from island to island. Middle Palaeolithic peoples demonstrate the earliest undisputed evidence for art and other expressions of abstract thought such as intentional burial of the dead.

From 35,000 to 10,000 years ago (the end of the last ice age) modern humans spread out further across the Earth during the period known as the Upper Palaeolithic. In the time when Cro-Magnon and Neanderthal traits mixed in Europe (35–24.5 ky) a relatively rapid succession of often complex stone artifact technologies took place. During period between 35 and 10 kya evolved: from 35 to 29 kya Chatelperronian, 32–26 Aurignacian, 28–22 Gravettian, 22–17 Solutrean, and 18–10 Magdalenian. The last two occurred after the disappearance of neanderthal traits from paleoantropological specimens.
The Americas were colonised via the Bering land bridge which was exposed during this period by lower sea levels. These people are called the Paleo-Indians, and the earliest accepted dates are those of the Clovis culture sites, some 13,500 years ago. Globally, societies were hunter-gatherers but evidence of regional identities begins to appear in the wide variety of stone tool types being developed to suit very different environments.