Domesticated barley (H. vulgare) is descended from wild barley(Hordeum spontaneum). Both forms are diploid (2n=14 chromosomes). As wild barley is interfertile with domesticated barley, the two forms are often treated as one species, divided into Hordeum vulgare subsp. spontaneum (wild) and subsp. vulgare (domesticated). The main difference between the two forms is the brittle rachis of the former, which enables seed dispersal in the wild. The earliest finds of wild barley come from EpiPaleolithic sites in the Levant, beginning in the Natufian. The earliest domesticated barley occurs at Aceramic Neolithic sites in the Near East such as the (PPN B) layers of Tell Abu Hureyra in Syria. Barley was one of the first crops domesticated in the Near East, at the same time as einkorn and emmer wheat.

Barley was, alongside emmer wheat, a staple cereal of ancient Egypt, where it was used to make bread and beer; together, these were a complete diet. The general name for barley is jt (hypothetically pronounced "eat"); šma (hypothetically pronounced "SHE-ma") refers to Upper Egyptian barley and is a symbol of Upper Egypt. According to Deuteronomy 8:8, barley is one of the "Seven Species" of crops that characterize the fertility of the Promised Land of Canaan, and barley has a prominent role in the Israelite sacrifices described in the Pentateuch (see e.g. Numbers 5:15).

In ancient Greece, the ritual significance of barley possibly dates back to the earliest stages of the Eleusinian Mysteries. The preparatory kykeon or mixed drink of the initiates, prepared from barley and herbs, was referred to in the Homeric hymn to Demeter, who was also called "Barley-mother".

Barley in Egyptian hieroglyphs jt barley determinative/ideogram

jt (common) spelling

šma determinative/ideogram

Greek practice was to dry the barley groats and roast them before preparing the porridge, according to Pliny the Elder's Natural History (xviii.72). This produces malt that soon ferments and becomes slightly alcoholic.

Tibetan barley has been the only major staple food in Tibet for centuries. It is made into a flour product called tsampa.

Palaeoethnobotanists have found that barley has been grown in the Korean Peninsula since the Early Mumun Pottery Period (c. 1500–850 BCE) along with other crops such as millet, wheat, and legumes (Crawford and Lee 2003).