At the most simple definition, mosaic is "a picture or other design constructed from smaller pieces". As well as the subject and style of the design, it is the choice of materials, plus the skill in creating and placing the pieces that contribute to the personal, artistic and practical value of the mosaic. A special feature is that the pieces are normally solid and durable. The physical qualities of the materials add greatly to the significance of the mosaic. Materials may be reflective or iridescent (glass, gold, mirror). Mosaics can be 3-dimensional, and can incorporate objects and unusual items.

The history of mosaic goes back some 4,000 years or more, with the use of terracotta cones pushed point-first into a background to give decoration. By the eighth century BC, there were pebble pavements, using different coloured stones to create patterns, although these tended to be unstructured decoration. It was the Greeks, in the four centuries BC, who raised the pebble technique to an art form, with precise geometric patterns and detailed scenes of people and animals.

In the rest of Europe, mosaic went into general decline throughout the Middle Ages. However a flourishing tile industry led to mosaic tiling patterns in abbeys and other major religious buildings, for example. These tiles from Prior Crauden's Chapel at Ely Cathedral date from around 1320. The floor of the Chapel features a detailed tiled scene of Adam and Eve.

The Art Nouveau movement also embraced mosaic art. In Barcelona, Antoni Gaudi worked with Josep Maria Jujol to produce the stunning ceramic mosaics of the Guell Park (below) in the first two decades of the 20th century.

Mosaic is in a healthy state in the early 21st century, despite a tendency for it to be thought of as more the work of craftspeople than artists. Perhaps this is a difficulty in accepting the fact that mosaics often have a dual function, for example as flooring, and also because it is a very accessible, non-elitist form of creativity.