Description (through texts, images, models or samples) played a central role in the patent regimes that emerged in the eighteenth century, first in England, later in the United States and in France. Description ensured that the contract—protection in exchange for disclosure of the invention—justifying the existence of patents worked not only in theory but also in practice. Gradually, English and American “specifications” and French “mémoires descriptifs et explicatifs” fed into a large body of technological literature, with the distinctive feature that this literature was (in principle) written by the inventors themselves. This article explores the styles and techniques of representation which were used in patents, mainly in France, in comparison with the United States. The study of the diversity and evolution of these representations contributes not only to the history of patents and their uses, but also to the history of technological thinking in the nineteenth century.