Text messaging, or texting, is the act of composing and sending electronic messages, typically consisting of alphabetic and numeric characters, between two or more users of mobile phones, tablet computers, smartwatches, desktops/laptops, or another type of compatible computer. Text messages may be sent over a cellular network or may also be sent via satellite or Internet connection.

The term originally referred to messages sent using the Short Message Service (SMS) on mobile devices. It has grown beyond alphanumeric text to include multimedia messages using the Multimedia Messaging Service (MMS) and Rich Communication Services (RCS), which can contain digital images, videos, and sound content, as well as ideograms known as emoji (happy faces, sad faces, and other icons), and on various instant messaging apps. Text messaging has been an extremely popular medium of communication since the turn of the century and has also influenced changes in society.

Text messages are used for personal, family, work, business, and social purposes. In the 21st century, the sending of short informal messages became mainstream and an accepted part of many cultures, as happened earlier with emailing. Texting is a quick and easy way to communicate with friends, family, and colleagues, including in contexts where a call would be impolite or inappropriate (e.g., calling very late at night or when one knows the other person is busy with family or work activities). Like e-mail and voicemail, and unlike calls (in which the caller hopes to speak directly with the recipient), texting does not require the caller and recipient to both be available at the same moment; this permits communication between busy individuals. Text messages can also be used to interact with automated systems, for example, to order products or services from e-commerce websites or to participate in online contests. Advertisers and service providers use direct text marketing to send messages to mobile users about things like promotions and order status, instead of using postal mail, email, or voicemail.

The electrical telegraph systems, developed in the early 19th century, used electrical signals to send text messages. In the late 19th century, wireless telegraphy was developed using radio waves.

In 1933, the German Reichspost (Reich postal service) introduced the first "telex" service.

The University of Hawaii began using radio to send digital information as early as 1971, using ALOHAnet.^{[citation needed]}

Friedhelm Hillebrand conceptualised SMS in 1984 while working for Deutsche Telekom. Sitting at a typewriter at home, Hillebrand typed out random sentences and counted every letter, number, punctuation mark, and space. Almost every time, the messages contained fewer than 160 characters, thus giving the basis for the limit that one could type via text messaging. With Bernard Ghillebaert of France Télécom, he developed a proposal for the GSM (Groupe Spécial Mobile) meeting in February 1985 in Oslo. The first technical solution evolved in a GSM subgroup under the leadership of Finn Trosby. It was further developed under the leadership of Kevin Holley and Ian Harris (see Short Message Service). SMS forms an integral part of Signalling System No. 7 (SS7). Under SS7, it is a "state" with 160 characters of data, coded in the ITU-T "T.56" text format, that has a "sequence lead in" to determine different language codes and may have special character codes that permit, for example, sending simple graphs as text. This was part of ISDN (Integrated Services Digital Network), and since GSM is based on this, it made its way to the mobile phone. Messages could be sent and received on ISDN phones, and these can send SMS to any GSM phone. The possibility of doing something is one thing; implementing it is another, but systems existed in 1988 that sent SMS messages to mobile phones^{[citation needed]} (compare ND-NOTIS).

SMS messaging was used for the first time on 3 December 1992, when Neil Papworth, a 22-year-old test engineer, used a computer to send the text message "Merry Christmas" via the Vodafone network to the phone of Richard Jarvis, who was at a party in Newbury, Berkshire celebrating the event. Papworth later said, "it didn't feel momentous at all". Modern SMS text messaging is usually sent from one mobile phone to another. Finnish Radiolinja became the first network to offer a commercial person-to-person SMS text messaging service in 1994. When Radiolinja's domestic competitor, Telecom Finland (now part of TeliaSonera), also launched SMS text messaging in 1995 and the two networks offered cross-network SMS functionality, Finland became the first nation where SMS text messaging was offered on a competitive as well as a commercial basis. GSM was allowed in the United States, but the radio frequencies were blocked and awarded to US "Carriers" to use US technology, which limited development of mobile messaging services in the US. The GSM in the US had to use a frequency allocated for private communication services (PCS) – what the ITU frequency régime had blocked for DECT (Digital Enhanced Cordless Telecommunications) – a 1,000-foot range picocell, but it survived. American Personal Communications (APC), the first GSM carrier in America, provided the first text-messaging service in the United States. Sprint Telecommunications Venture, a partnership of Sprint Corp. and three large cable-TV companies, owned 49 percent of APC. The Sprint venture was the largest single buyer at a government-run spectrum auction that raised $7.7 billion in 2005 for PCS licenses. APC operated under the brand name Sprint Spectrum and launched its service on 15 November 1995, in Washington, D.C., and Baltimore, Maryland. Vice President Al Gore in Washington, D.C., made the initial phone call to launch the network, calling Mayor Kurt Schmoke in Baltimore.