Nomads are mobile tent-dwelling pastoralists in areas of the arid zone (which stretches from Morocco to China, with the area we call the Middle East at its center), where there is no urban or agricultural development. By migrating seasonally to find the best pastures, they are able to manage larger flocks. Unlike urban and agricultural communities, which are organized in terms of land and water ownership, and investment in water supplies, nomads are unable to organize investment or accumulate property in the same way as urban populations can, and are organized tribally, in terms of personal relations of descent, kinship, marriage connections and relative age.

Nomads milk and shear their animals, and are important producers of clarified butter and other milk products, as well as meat and wool, all of which they market in the settled communities where they get their bread, fruit, and vegetables. The two economies have always been reciprocally inter-related, and their interdependence was important for the rural (and to some extent also the urban) economies well into the 20th century.

Unlike the settled populations, for whom land and water are long-term investments, nomads depend on their flocks, mostly sheep and goats, which have a ten-year productive life span, and reproductive rates that vary year by year. The two groups are also ideologically opposed. Urban disdain for nomads and their lifestyle is known from as far back as Sumerian texts, and the nomadic groups often see the property of the cities as a potential resource. It is easy for them to take advantage of new opportunities, such as, in some cases, raiding trading caravans or villages. There are even examples of nomads taking over the government of a city. But there have also been exchanges of population between nomadic and urban communities. Nomads could be recruited as additional labor in the cities in an economic boom. Urban laborers and villagers may have joined the nomads when there were problems in the rural or urban economies.