Mud is one of the oldest construction materials. It is still used today in a number of countries and it is estimated that 30 per cent of all habitations worldwide are built with mud. The architecture and construction technology developed for this material are extremely varied because they depend on the materials found locally, the extent of the local technology, and the social and cultural background. The first part of this article deals with the various technologies used by craftsmen, the architecture they have developed, and the technical solutions adopted for construction in different countries. The second part of this article concerns the principle causes of the deterioration of such buildings and the methods used for their restoration. -- ICCROM