Zend_Validate_Alpha allows you to validate if a given value contains only alphabetical characters. There is no length limitation for the input you want to validate. This validator is related to the Zend_Validate_Alnum validator with the exception that it does not accept digits. The following options are supported for Zend_Validate_Alpha: allowWhiteSpace: If whitespace characters are allowed. This option defaults to FALSE A basic example is the following one: isValid('Abcd')) { // value contains only allowed chars } else { // false } ]]> Per default whitespaces are not accepted because they are not part of the alphabet. Still, there is a way to accept them as input. This allows to validate complete sentences or phrases. To allow the usage of whitespaces you need to give the allowWhiteSpace option. This can be done while creating an instance of the validator, or afterwards by using setAllowWhiteSpace(). To get the actual state you can use getAllowWhiteSpace(). true)); if ($validator->isValid('Abcd and efg')) { // value contains only allowed chars } else { // false } ]]> When using Zend_Validate_Alpha then the language which the user sets within his browser will be used to set the allowed characters. This means when your user sets de for german then he can also enter characters like ä, ö and ü additionally to the characters from the english alphabet. Which characters are allowed depends completly on the used language as every language defines it's own set of characters. There are actually 3 languages which are not accepted in their own script. These languages are korean, japanese and chinese because this languages are using an alphabet where a single character is build by using multiple characters. In the case you are using these languages, the input will only be validated by using the english alphabet.