The maritime economy can be defined as the whole range of activities related to the sea, in other words whose conditions of development depend on the sea. This factual definition needs to be specified according to the degree of dependence: total, for the entire production mode, or partial, for the manufacturing of certain products or the supply of certain services. Furthermore, the definition raises a series of questions. A question of coverage: is it possible to list and delineate the whole range of "maritime" economic activities? A question of measuring the economic value of this range: is it possible to give a definition and a quantitative assessment of this range? By means of which indicators? A question of coherence: is the whole range composed of activities unrelated to each other? Or do they have commercial relationships and conditions of development (environmental, regulatory) leading, to a certain extent, to consider them jointly? The present chapter aims to address these issues on a European scale.