This research addresses the problem of inter-system authentication in multi-network environments. In such environments, allowing users to roam seamlessly between multiple types of networks creates problems for network security. There is currently no means to transfer the identity or trust record of a user that roams between networks. For example, in 2G and 3G cellular systems, the authentication of mobile users is accomplished through user registration. However, current registration techniques assume a centralized authentication authority, which is not suitable for the distributed, multi-network environment. In addition, registration research traditionally focuses on location update and paging schemes, leaving the new authentication and security issues unresolved. This proposal addresses the problem of inter-system authentication in multi-network environments, by following the research agenda in the design and architectural dimensioning of an inter-system authentication agent (ISA), as well as in the design of the so-called passport and visa mechanism to issue permissions (or service denials) to roaming users. In addition, the project will develop an inter-system registration protocol based on the passport/visa system and evaluate the performance of a cost-benefit analysis for the ISA architecture and the passport/visa system. This project will advance the field where the authentication of unknown users is an issue. In particular, the success of this project will have an impact on distributed computing research, such as the buying and selling of computing resources over the Internet, shared information grids for scientific and engi-neering applications, and the development of techniques for secure transaction processing.