Information is the main value of Information Society. The recent developments in computing power and telecommunications, along with the constant drop of Internet access costs and data management and storing, created the right conditions for the global diffusion of the Web and, more generally, of new research tools able to analyze information and their contents. Depending on the particular application scenario and on the type of information that has to be managed and searched, different techniques need to be devised. In this book, the author deals with the two most common types of information: plain text, discussed in the first part, and semi-structured data, in particular XML documents, deeply discussed the second part. The detailed analysis of approximate matching, duplicate document detection, exact, approximate and semantic query answering, multi-version document management and personalized access techniques offered in this book will guide Information Technology professionals and users in effectively and efficiently managing information and knowledge, thus answering the increasingly complex Information needs of most 21st century applications.