In Spain the formal identity number on an ID card is the most important piece of identification. It is used in all public and private transactions. It is required to open a bank account, to sign a contract, to have state insurance and to register at a university and should be shown when being fined by a police officer. It is one of the official documents required to vote at any election, although any other form of official ID such as a driving licence or passport may be used. The card also constitutes a valid travel document within the European Union.