Relief is a sculptural method in which the sculpted pieces remain attached to a solid background of the same material. The term relief is from the Latin verb relevare, to raise (lit. 'to lift back'). To create a sculpture in relief is to give the impression that the sculpted material has been raised above the background plane. When a relief is carved into a flat surface of stone (relief sculpture) or wood (relief carving), the field is actually lowered, leaving the unsculpted areas seeming higher. The approach requires chiselling away of the background, which can be time-intensive. On the other hand, a relief saves forming the rear of a subject, and is less fragile and more securely fixed than a sculpture in the round, especially one of a standing figure where the ankles are a potential weak point, particularly in stone. In other materials such as metal, clay, plaster stucco, ceramics or papier-mâché the form can be simply added to or raised up from the background. Monumental bronze reliefs are made by casting.

There are different degrees of relief depending on the degree of projection of the sculpted form from the field, for which the Italian and French terms are still sometimes used in English. The full range includes high relief (Italian alto-rilievo, French haut-relief), where more than 50% of the depth is shown and there may be undercut areas, mid-relief (Italian mezzo-rilievo), low relief (Italian basso-rilievo, French: bas-relief), and shallow-relief (Italian rilievo schiacciato), where the plane is only very slightly lower than the sculpted elements. There is also sunk relief, which was mainly restricted to Ancient Egypt (see below). However, the distinction between high relief and low relief is the clearest and most important, and these two are generally the only terms used to discuss most work.

The definition of these terms is somewhat variable, and many works combine areas in more than one of them, rarely sliding between them in a single figure; accordingly some writers prefer to avoid all distinctions. The opposite of relief sculpture is counter-relief, intaglio, or cavo-rilievo, where the form is cut into the field or background rather than rising from it; this is very rare in monumental sculpture. Hyphens may or may not be used in all these terms, though they are rarely seen in "sunk relief" and are usual in "bas-relief" and "counter-relief". Works in the technique are described as "in relief", and, especially in monumental sculpture, the work itself is "a relief".

Reliefs are common throughout the world on the walls of buildings and a variety of smaller settings, and a sequence of several panels or sections of relief may represent an extended narrative. Relief is more suitable for depicting complicated subjects with many figures and very active poses, such as battles, than free-standing "sculpture in the round". Most ancient architectural reliefs were originally painted, which helped to define forms in low relief. The subject of reliefs is for convenient reference assumed in this article to be usually figures, but sculpture in relief often depicts decorative geometrical or foliage patterns, as in the arabesques of Islamic art, and may be of any subject.

Rock reliefs are those carved into solid rock in the open air (if inside caves, whether natural or human-made, they are more likely to be called "rock-cut"). This type is found in many cultures, in particular those of the Ancient Near East and Buddhist countries. A stele is a single standing stone; many of these carry reliefs.

The distinction between high and low relief is somewhat subjective, and the two are very often combined in a single work. In particular, most later "high reliefs" contain sections in low relief, usually in the background. From the Parthenon Frieze onwards, many single figures in large monumental sculpture have heads in high relief, but their lower legs are in low relief. The slightly projecting figures created in this way work well in reliefs that are seen from below, and reflect that the heads of figures are usually of more interest to both artist and viewer than the legs or feet. As unfinished examples from various periods show, raised reliefs, whether high or low, were normally "blocked out" by marking the outline of the figure and reducing the background areas to the new background level, work no doubt performed by apprentices (see gallery).

A low relief is a projecting image with a shallow overall depth, for example used on coins, on which all images are in low relief. In the lowest reliefs the relative depth of the elements shown is completely distorted, and if seen from the side the image makes no sense, but from the front the small variations in depth register as a three-dimensional image. Other versions distort depth much less. The term comes from the Italian basso rilievo via the French bas-relief (French pronunciation: [baʁəljɛf]), both meaning "low relief". The former is now a very old-fashioned term in English, and the latter term is becoming so.

Low relief is a technique which requires less work than high relief, and is therefore cheaper to produce, as less of the background needs to be removed in a carving, or less modelling is required. In the art of Ancient Egypt, Assyrian palace reliefs, and other ancient Near Eastern and Asian cultures, a consistent very low relief was commonly used for the whole composition. These images would usually be painted after carving, which helped define the forms; today the paint has worn off in the great majority of surviving examples, but minute, invisible remains of paint can usually be discovered through chemical means.