O2 (brand)

O2 (typeset as O₂) is a British brand owned by Spanish telecommunications company Telefónica, used for its subsidiaries in the United Kingdom and Germany, its former subsidiaries in the Czech Republic and Slovakia, and since 2018 as an online-only flanker brand in Spain. The O2 brand was created by British Telecom (BT) in 2001 ahead of the demerger of its global BT Wireless division as mmO2 plc (later O2 plc).

BT Wireless provided telecommunications services in the United Kingdom (BT Cellnet), Ireland (Digifone), Germany (VIAG Interkom), the Netherlands (Telfort), the Isle of Man (Manx Telecom), and a global mobile data business known as Genie Internet. Most of these operations were rebranded as O2 following the demerger from BT. In 2006, O2 plc was acquired by Telefónica, becoming Telefónica Europe. As part of a reorganisation of Telefónica in 2014, Telefónica Europe's holdings and operations became direct subsidiaries of its parent: Telefónica S.A.

Today, the O2 brand is used primarily in the United Kingdom, Germany, the Czech Republic, Slovakia, and Spain. In the United Kingdom, O2 is the largest mobile network by customer base, and since 2021 has formed part of Virgin Media O2—a 50:50 joint venture between Telefónica and Liberty Global. It has held the naming rights to the O2 Arena in London since 2007, a partnership with Live Nation covering branding and priority access to customers for the Academy Music Group venues since 2008, and been long-time sponsors of England Rugby (since it was BT Cellnet). In Germany, O2 functions as Telefónica's flagship brand, offering broadband, landline, and mobile services. The O2 Czech Republic and Slovakia networks were acquired by Telefónica in 2005 and branded O2. These businesses were sold by Telefónica in 2013, but continue to license the brand. In Spain, O2 is an online-only flanker brand of Telefónica subsidiary Movistar.