T-Mobile is the brand name used by some of the mobile communications subsidiaries of the German telecommunications company Deutsche Telekom AG in the Czech Republic (T-Mobile Czech Republic), Poland (T-Mobile Polska), the United States (T-Mobile US) and by the former subsidiary in the Netherlands (T-Mobile Netherlands).

The T-Mobile brand was introduced in 1996 and the name was previously used by subsidiaries in other countries, including Austria (now Magenta), Croatia (now Hrvatski Telekom), Germany (now Deutsche Telekom), Hungary (now Magyar Telekom), Montenegro (now Crnogorski Telekom), North Macedonia (now Makedonski Telekom), Romania (now Telekom România), Slovakia (now Slovak Telekom), and the United Kingdom (now EE Limited).

In 1999, Deutsche Telekom formed the holding company T-Mobile International AG for its mobile communications subsidiaries. From 2003 to 2007, T-Mobile International was one of Deutsche Telekom's services, in addition to "Broadband/Fixnet", "Business Customers" and "Group HQ and Shared Services". In 2009, Deutsche Telekom transformed its structure to adopt a regional setup (Germany, Europe, US). By combining its previously separated fixed and mobile subsidiaries to form integrated local businesses, T-Mobile International itself was merged into Deutsche Telekom AG.

When T-Mobile International AG existed, the holding company was based in Bonn, Germany, and its subsidiaries operated GSM-, UMTS- and LTE-based cellular networks in Europe, the United States, Puerto Rico and the U.S. Virgin Islands. The company had financial stakes in mobile operators in both Central and Eastern Europe. Globally, T-Mobile International's subsidiaries had a combined total of approximately 230 million subscribers. It was the world's thirteenth-largest mobile-phone service provider by subscribers, and the fourth-largest multinational after the UK's Vodafone, India's Airtel, and Spain's Telefónica.