In recent years there has been an increasing research interest in the problem of contextualizing search to the aim of overcoming the limitations of the “one size fits all” paradigm, which is generally applied by Search Engines and Information Retrieval Systems (IRSs). By this paradigm the keyword-based query is considered as the only carrier of the users’ information needs. As a consequence, the relevance estimate is system-centered, as the user context is not taken into account. Instead, a contextual Search Engine or IRS relies on a user-centered approach since it involves processes, techniques and algorithms that exploit as much contextual factors as possible in order to tailor the search results to users