Telefónica, S.A., ( , , , , , ) is a Spanish telecommunication company. Operating globally, it is one of the largest fixed-line and mobile telecommunications companies in the world: 2nd in terms of number of clients (with the acquisition of O2 plc., Movistar and Manx Telecom) only behind a Chinese mobile provider, and in the top five in market value. They were behind China Mobile, AT&T, and Vodafone in November 2007.

Created in 1924, until liberalization of the telecom market in 1997 Telefónica was the only telephone operator in Spain and still holds a dominant position, over 75% in 2004. Since 1997, the Spanish government has privatised its interest in the company. On 5th July, 2007, the European Commission ordered Telefónica to pay a record antitrust fine of almost €152 million for activities in the Spanish broadband market that "harmed Spanish consumers, Spanish businesses and the Spanish economy as a whole, and by extension Europe's economy", as said by European Union competition commissioner Neelie Kroes.