XML (Extensible Mark-up Language) databases are an active research area. The topic of security in XML databases is important as it includes protecting sensitive data and providing a secure environment to users. Trust based access is an established technique in many fields, such as networks and distributed systems, but it has not previously been used for XML databases. In Trust Based Access Control, user privileges are calculated dynamically depending on the user’s behaviour. In this thesis, the novel idea of applying Trust Based Access Control (TBAC) for XML databases has been developed. This approach improves security and provides dynamic access control for XML databases. It manages access policy depending on users’ trustworthiness and prevents unauthorised processes, malicious transactions, and misuse from both outsiders and insiders. A practical Trust Based Access Control system for XML databases was evaluated. The dynamic access control has been tested from security, scalability, functionality, performance, and storage perspectives. The experimental results illustrate the flexibility of Trust Values and the scalability of the system with small to large XML databases and with various numbers of users. The results show that the main research idea of this study is worth pursuing and the system could be developed further.