The term “evaluating written language” hides underlying polysemic concepts that this article aims at clarifying from the start. Therefore both the certifying and the formative evaluation of written production will be addressed. The former is doubly institutional: its aim is to give an orientation and a planification of learning writing skills, and also constitutes the basis of the final decision of success or failure. The latter, widely claimed but less widely applied, aims to improve the learning of the skill during the learning, and is based on diagnostic concepts, and, in coherence with those, on the setting up of permanent actions allowing learners to progress in their learning. These aspects will be illustrated by concrete examples.