This text is an introduction to a collective book on language science applications and implications, the following lines of which are taken from the 4th cover: The objects, terrain and theories of linguists are multiple. This plurality is accompanied by a plurality of possible positions and applications. In the Anglo-Saxon world, the highly developed field of ‘applied Linguistic’ — from didactic to terminology, speech analysis, acquisition, corpus linguists or computer-aided design — covers the full social impact of language sciences. The same is not true in France, where the discussion in this area seems to me to be little theorised. What do we do when we intervene? What do we do when you go on the ground to obtain data, offer a “feedback to actors” or transmit results when you teach, advise or expertise? For whom, what are we doing, to what extent can we go or want to go during language interventions? What theoretical and epistemological tools are needed? How can the trap of irrational “applicationism” be avoided? The generalisation of interventions also means the emergence of language science related occupations. What training courses can be envisaged for these professions? What gaps between requests on the ground and linguists’ proposals? How to manage them? Here are some of the questions raised by this book.