Abstract: This specification describes technologies relating to applying electronic signatures to content items. In general, one aspect of the subject matter described in this specification can be embodied in methods that include receiving a content item and receiving a request to electronically sign the content item by a user by associating the content item with a credential associated with the user, the request comprising data identifying the credential from among a set of credentials that are associated with the user. The method may further include generating a package comprising the content item and data for the identified credential.