For nearly 30 years, Mesolithic period in northern France has been characterised by the dynamism of his rescue archaeology. Indeed, in recent years, several excavations have notably renewed our knowledge about the organisation and function of Mesolithic open-air sites, both for Early and Late Mesolithic. This is due in particular to the extensive character of excavations (over several thousand square metres), the methods used (planimetric and manual digging, georeferencing of remains, etc.) as well as the technological and use-wear studies of lithic material undertaken in this framework. Detailed analysis of the lithic material and dates show that most sites are the result several episodes of occupations sometimes spread over several hectares. But refits also shows the existence of real camps, connecting together several occupation units. At the same time, lithic use-wear analysis enable us to better identify the spatial organisation of Mesolithic occupations by identifying differentiated functional spaces within the concentrations and on their periphery. These concentrations are characterised by areas related to knapping activities, arrowheads manufacture and sometimes by fire practices. Other activities are regularly identified in these zones in association with more discrete and peripheric spaces that also provide lithic remains with use traces (skin working, butchery, plant working, etc.), scattered faunal remains, combustion structures (fireplaces or garbage dumps), pits... Burials are also quite frequently discovered but rarely associated with contemporaneous occupations in the surroundings. All these areas, generally located at a distance from the main concentrations, can only be identified by an extensive and careful exploration around the concentrations. These excavation strategies are not always in line with economic interests and sometimes questioned. But it is at this price that we can understand the complex spatial and functional configuration of Mesolithic occupations and thus better define the last hunters-gatherers mobility and lifestyles.