With the emergence of the World Wide Web and online businesses, business¿ XML databases are increasingly being queried directly by users. This book focuses on three aspects related to querying of XML data, as follows: (1) Improving accuracy of XML keyword queries by modeling the contexts of XML elements. Most current research is focused on building relationships between data elements based solely on their labels and proximity to one another, while overlooking the contexts of the elements. This may lead to erroneous results. This book presents different context-driven techniques that avoid this problem. (2) Enhancing XML-based personalized search by using group profiling to determine individual preferences. Group profiling can be an efficient retrieval mechanism, where a user profile is inferred from the profile of the social groups to which the user belongs. A social group is defined based on ethnic, cultural, religious, or other characteristics. (3) Improving performance of distributed XML querying by caching of frequently-used query results. For each of these areas, we developed formal concepts and algorithms that lead to the improved accuracy and performance.