Zend_Validate_Iban validates if a given value could be a IBAN number. IBAN is the abbreviation for "International Bank Account Number". The following options are supported for Zend_Validate_Iban: locale: Sets the locale which is used to get the IBAN format for validation. IBAN numbers are always related to a country. This means that different countries use different formats for their IBAN numbers. This is the reason why IBAN numbers always need a locale. By knowing this we already know how to use Zend_Validate_Iban. We could use the application wide locale. This means that when no option is given at initiation, Zend_Validate_Iban searches for the application wide locale. See the following code snippet: isValid('AT611904300234573201')) { // IBAN appears to be valid } else { // IBAN is not valid } ]]> Of course this works only when an application wide locale was set within the registry previously. Otherwise Zend_Locale will try to use the locale which the client sends or, when non has been send, it uses the environment locale. Be aware that this can lead to unwanted behaviour within the validation. Sometime it is usefull, just to validate if the given value is a IBAN number or not. This means that you don't want to validate it against a defined country. This can be done by using a FALSE as locale. false)); // Note: you can also set a FALSE as single parameter if ($validator->isValid('AT611904300234573201')) { // IBAN appears to be valid } else { // IBAN is not valid } ]]> So any IBAN number will be valid. Note that this should not be done when you accept only accounts from a single country. To validate against a defined country, you just need to give the wished locale. You can do this by the option locale and also afterwards by using setLocale(). 'de_AT')); if ($validator->isValid('AT611904300234573201')) { // IBAN appears to be valid } else { // IBAN is not valid } ]]> You must give a full qualified locale, otherwise the country could not be detected correct because languages are spoken in multiple countries.