Clay is a finely-grained natural rock or soil material. It combines one or more clay minerals with possible traces of quartz (SiO₂), metal oxides (Al₂O₃, MgO etc.) and organic matter.

Clay is one of the oldest building materials on Earth. It was and is used among other ancient, naturally-occurring geologic materials such as stone and organic materials like wood. More than half of the world’s population still live or work in buildings made with clay. This is valid in both, traditional societies as well as developed countries.

Clay is the primary ingredient in many natural building techniques. It is used to create adobe, cob, cordwood, and rammed earth structures. Building elements such as wattle and daub, clay plaster, clay render case, clay floors and clay paints and ceramic building material are made of clay.