Nowadays, personal data is stored at very diverse places. Consider, for instance, the emails handled by free web mail services, the personal preferences in an Ambient Intelligence setting, or medical data (e.g. the Dutch electronic patient record). In our increasingly connected world, personal data is often outsourced to external servers, some servers may even be in other countries. This development raises concerns about the security and privacy of those data. The results of this project will allow us to address these concerns by storing the data in an encrypted format such that unauthorized parties (the storage server may even be one of them) cannot read the data, while still allowing efficient querying of the data by authorized parties. Building trust and confidence as well as enabling secure data access is paramount in this setting. With XML becoming the dominant standard for describing and exchanging data, a huge amount of XML-formatted data is being produced, outsourced, and manipulated by different applications across multiple enterprizes on the Internet. The need to protect outsourced data from being disclosed and/or tampered with is growing rapidly. A typical technique for achieving security is to distribute and outsource data in encrypted form. However, this usually implies that one has to sacrifice efficiency for the obtained security. In this project, we aim to bring the worlds of security and data management closer to each other. In particular, we will focus on efficient querying of encrypted XML data, where the major challenge lies in the development of techniques that deal with the seemingly contradictory requirements of security and efficiency. The main objective of this project is to build a multi-user database system capable of searching in encrypted data with powerful nested query capabilities.