Introduction: Ways and Means to deal with data from Multiple Sources

To introduce and frame the content of the following chapters, here the main motivation for using data fusion, the different definitions and the different context of applications are illustrated. The overview follows the most diffuse taxonomy, which classifies the data fusion approaches in low, mid and high-level. At the same time the link between data fusion and multiblock/multiset methods is underlined aiming at furnishing a unified view of the field.