Public key certification provides mechanisms that can be used to build truly scaleable security services, such as allowing people who have never met to have assurance of each other's identity. Authentication involves syntactic verification of a certificate chain followed by a semantic look at the policies under which the certificates were issued. This results in a level of assurance that the identity of the person to be authenticated is an accurate description of the person involved, and requires verifiers to specify who they trust and what they trust them to do. Two widely discussed mechanisms for specifying this trust, the PEM and PGP trust models, approach the problem from fundamentally different directions. The EC funded ICE-TEL project, which is deploying a security infrastructure and application set for the European research community, has described a new trust model that attempts to be equally applicable to organisation-centric PEM users and user-centric PGP users.