Cloisonné (French: [klwazɔne]) is an ancient technique for decorating metalwork objects with colored material held in place or separated by metal strips or wire, normally of gold. In recent centuries, vitreous enamel has been used, but inlays of cut gemstones, glass and other materials were also used during older periods. Cloisonné enamel was probably developed as an easier imitation of cloisonné work using gems. The resulting objects can also be called cloisonné.

The decoration is formed by first adding compartments (cloisons in French) to the metal object by soldering or affixing silver or gold as wires or thin strips placed on their edges. These remain visible in the finished piece, separating the different compartments of the enamel or inlays, which are often of several colors. Cloisonné enamel objects are worked on with enamel powder made into a paste. The objects are fired in a kiln for finishing. If gemstones or colored glass are used, the pieces need to be cut or ground into the shape of each cloison.

In antiquity, the cloisonné technique was mostly used for jewellery and small fittings for clothes, weapons, or similar small objects decorated with geometric or schematic designs, with thick cloison walls. In the Byzantine Empire, techniques using thinner wires were developed to allow more pictorial images to be produced. These were mostly used for religious images and jewellery, and by then always using enamel. This was used in Europe, especially in Carolingian and Ottonian art. By the 14th century this enamel technique had been replaced in Europe by champlevé. By then, cloisonne technique had spread to China, where it was soon used for much larger vessels such as bowls and vases. The technique remains common in China to the present day. From the 18th century, artisans in the West produced cloisonné enamel objects using Chinese-derived styles.

In Middle Byzantine architecture cloisonné masonry refers to walls built with a regular mix of stone and brick, often with more of the latter. The 11th or 12th-century Pammakaristos Church in Istanbul is an example.

Cloisonné first developed in the jewellery of the ancient Near East, and the earliest works with enamel all used the cloisonné technique, placing the enamel within small cells with gold walls. This had been used as a technique to hold pieces of stone and gems tightly in place since the 3rd millennium BC, for example in Mesopotamia, and later in Egypt. Enamel seems likely to have developed as a cheaper method of achieving similar results.

The earliest surviving undisputed objects known to use enamel are a group of Mycenaean rings from a tomb in Cyprus, dated to the 12th century BC, which used very thin wire.

In the jewellery of ancient Egypt, including the pectoral jewels of the pharaohs, thicker strips form the cloisons, which remain small. In Egypt gemstones and enamel-like materials (sometimes called "glass-paste") were both used. Although Egyptian pieces, including jewellery from the Tomb of Tutankhamun of c. 1325 BC, are frequently described as using "enamel", many scholars doubt that the glass paste was sufficiently melted to be properly so described, and use terms such as "glass-paste". It seems possible that in Egyptian conditions the melting point of the glass and gold were too close to make enamel a viable technique. Nonetheless, there appear to be a few actual examples of enamel, perhaps from the Third Intermediate Period of Egypt (beginning 1070 BC) on. But it remained rare in both Egypt and Greece.

The technique appears in the Koban culture (c. 1200 to 350 BC) of the northern and central Caucasus, and was perhaps carried by the Sarmatians to the ancient Celts, but they essentially used the champlevé technique. Subsequently, enamel was just one of the fillings used for the small, thick-walled cloisons of the Late Antique and Migration Period styles. At Sutton Hoo, the Anglo-Saxon pieces (dated to the 6th or 7th centuries AD) mostly use garnet cloisonné, but this is sometimes combined with enamel in the same piece. A problem that adds to the uncertainty over early enamel is artefacts (typically excavated) which appear to have been prepared for enamel, but which have now lost whatever filled the cloisons. This occurs in several different regions, from ancient Egypt to Anglo-Saxon England. Once enamel becomes more common, as in medieval Europe after about 1000, the assumption that enamel was originally used becomes safer.