Context Mediation is a field of research that is concerned with the interchange of information across different environments, which provides a vehicle to bridge semantic gaps among disparate entities. Knowledge Discovery is concerned with the extraction of actionable information from large databases. A challenge that has received relatively little attention is knowledge discovery in a highly disparate environment, that is multiple heterogeneous data sources, multiple domain knowledge sources and multiple knowledge patterns. This thesis tackles the problem of semantic interoperability among data, domain knowledge and knowledge patterns in a knowledge discovery process using context mediation. All presented techniques, methods and models are applied in real-world scenarios, covering disciplines from a wide range of industry, namely web mining and marketing, manufacturing, meteorology and internationalisation. When feasible, industry standards were utilised, for instance ODMG, PMML and KQML.The carried out research has resulted in almost fifty international publications, including the co-authorship of a book, a journal editorship and one conference best paper award.