Celesstin, a system that converts mechanical engineering drawings into a format suitable for CAD, is described. Celesstin integrates several modules in a blackboard-based interpretation system. Once a drawing has been digitized, a first processing step separates the text and the dimensioning lines from the pure graphics part. Celesstin vectorizes the graphics part and assembles the resulting lines into blocks, the basic elements for the technical entities that it creates. The result is transferred to the CAD system. Celesstin tries to match the extracted entities with the corresponding models from the CAD library. It puts the remaining blocks and lines into different layers of the CAD description. The system is based on the assumption that even when the vectorized drawing is distorted, it can be correctly interpreted by using knowledge about the representation rules used in technical drawings and about the manufacturing technology associated with the represented objects.