Short Message Service (SMS) is a text messaging service component of most telephone, Internet and mobile device systems. It uses standardized communication protocols that let mobile phones exchange short text messages, typically transmitted over cellular networks.

Developed as part of the GSM standards, and based on the SS7 signalling protocol, SMS rolled out on digital cellular networks starting in 1993 and was originally intended for customers to receive alerts from their carrier/operator. The service allows users to send and receive text messages of up to 160 characters, originally to and from GSM phones and later also CDMA and Digital AMPS; it has since been defined and supported on newer networks, including present-day 5G ones. Using SMS gateways, messages can be transmitted over the Internet through an SMSC, allowing communication to computers, fixed landlines, and satellite. MMS was later introduced as an upgrade to SMS with "picture messaging" capabilities.

In addition to recreational texting between people, SMS is also used for mobile marketing (a type of direct marketing), two-factor authentication logging-in, televoting, mobile banking (see SMS banking), and for other commercial content. The SMS standard has been hugely popular worldwide as a method of text communication: by the end of 2010, it was the most widely used data application with an estimated 3.5 billion active users, or about 80% of all mobile phone subscribers. More recently, SMS has become increasingly challenged by newer proprietary instant messaging services; RCS has been designated as the potential open standard successor to SMS.