In economics, groups of consumers in which the utility derived from consumption of certain goods or services increases as additional consumers purchase the same goods and services. Networks emerge if these particular goods or services have little or no value in isolation, and generate more value when more consumers use the same goods and services. Many products are required to be used with other products at the same time. A market characterized by such properties is called a network market in which there exist positive consumption externalities termed network externalities. A typical example of a network industry is telecommunications.