The present publication analyses the main legal issues arising out of the use of electronic signatures and authentication methods in international transactions. Part one provides an overview of methods used for electronic signature and authentication and their legal treatment in various jurisdictions. Part two considers the use of electronic signature and authentication methods in international transactions and identifies the main legal issues related to cross-border recognition of such methods. It has been observed that, from an international perspective, legal difficulties are more likely to arise in connection with the cross-border use of electronic signature and authentication methods that require the involvement of third parties in the signature or authentication process. This is the case, for instance, of electronic signature and authentication methods supported by certificates issued by a trusted third-party certification services provider, in particular digital signatures under a public key infrastructure (PKI). For this reason, part two of this publication devotes special attention to international use of digital signatures under a PKI. This emphasis should not be understood as a preference or endorsement of this or any other particular type of authentication method or technology.