Global System for Mobile Communications, originally Groupe Sp├ęcial Mobile, (GSM) is a standard that describes technologies for 2G cellular networks. On July 1, 1991, Finnish Prime Minister Harri Holkeri made the world's first GSM call (see the video below) to Kaarina Suonio (mayor in city of Tampere). Today, the technology is thus 20 years old.

Early European analog cellular networks employed technologies and protocols that varied from country to country, preventing interoperability of subscriber equipment and increasing complexity for equipment manufacturers. GSM was adopted in 1987 as the European standard for digital mobile technology when 15 representatives from 13 European countries signed a memorandum of understanding to develop and deploy a common cellular telephone system across the continent. Phase I of the GSM specification was published in 1990.

GSM was developed as a replacement for first generation analog cellular networks. The GSM standard originally described a digital circuit switched network optimized for full duplex voice telephony, but was expanded over time to include first circuit switched data transport, then packet data transport via GPRS. Packet data transmission speeds were later increased via EDGE. The GSM standard is succeeded by the 3G UMTS standard developed by the 3GPP. GSM networks are currently evolving further as they begin to incorporate 4G LTE Advanced standards.

GSM's high-quality voice calls, easy international roaming and support for services like text messaging (SMS) laid the foundations for a worldwide boom in mobile phone use. The GSM Association, which owns the GSM trademark, estimates that technologies defined in the GSM standard serve 80 percent of the global mobile market, encompassing more than 1.5 billion people across more than 212 countries and territories. In other words, GSM is the most ubiquitous standard for cellular networks.