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.