Recognition of identities and certainty about identity ownership are crucial factors for secure communication in digital environments. Identity Management Systems have been designed to aid users as well as organisations to manage different user identities. However, traditional Identity Management Systems are primarily designed to facilitate the management of identities from the perspective of the service provider, but provide little support on the user side to manage organisational identities. Public Key Infrastructures (PKI) is the primary tool in aiding users to manage such identities on their sides as well as to establish trust during online transactions. Nevertheless, the complexities and difficulties involved in managing and understanding such certificates from the general public’s point of view are overlooked. This causes vulnerabilities that open up for serious attacks such as identity theft and Phishing. Petname Systems have been proposed for managing organisational identities on the user side in order to improve the user friendliness and to strengthen security. This chapter provides an analysis of the Petname Model by describing its history and background, properties, application domains, and usability issues, and explains how a Petname System can be effectively combined with the PKI to recognise identities and impose certainty by validating the user trust on those identities. The chapter also presents an analysis on two applications that integrate the Public Key Infrastructure with the Petname Model.