Article describes the extreme fragility of old transparent paper, and a study of the techniques of manufacture of transparent paper from the Middle Ages to the present. Microscopical fiber analyses give interesting information on the composition of these papers. Research on fillers was conducted, but on such a limited amount of samples as to preclude drawing significant conclusions. Cleaning, deacidification, and lining are presented as possible restoration techniques. In addition to the usual requirements of innocuousness, stability, and reversibility, treatments must taken into account the special nature of these papers, and respect their dimensional stability and their transparency.