We discuss how references and citations within a document to particular sources can be verified and guaranteed. When a document refers through a quotation to another document, the reader should be able to verify that the reference is correct and that any quotation correctly represents the original text. The mechanism we describe enables the authentication of such quotations. It consists of: • A notation to be used when expressing quotations. This notation allows a controlled degree of freedom to make alterations from the original text. • Different means to check the correctness of such quotations with respect to the cited documents and to quotation rules. Categories and Subject Descriptors I.7.4 [Document and Text Processing]: Document Preparation—hypertext/hypermedia, markup languages General Terms Documentation Keywords citation, information trust