Longquan celadon (Chinese: 龙泉青瓷) is a type of green-glazed Chinese ceramic, known in the West as celadon or greenware, produced from about 950 to 1550. The kilns were mostly in Lishui prefecture in southwestern Zhejiang Province in the south of China, and the north of Fujian Province. Overall a total of some 500 kilns have been discovered, making the Longquan celadon production area one of the largest historical ceramic producing areas in China. "Longquan-type" is increasingly preferred as a term, in recognition of this diversity, or simply "southern celadon", as there was also a large number of kilns in north China producing Yaozhou ware or other Northern Celadon wares. These are similar in many respects, but with significant differences to Longquan-type celadon, and their production rose and declined somewhat earlier.

Celadon production had a long history at Longquan and related sites, but it was not until the Northern Song (960–1127) period that large-scale production began, and the move of the capital to Hangzhou, close to Longquan, after the start of the Southern Song (1127–1279), was probably important in the great expansion of both quality and production there. Both continued at high levels in the Yuan (1271–1368) and the early part of the Ming (1368–1644) periods. Longquan celadons were an important part of China's export economy for over five hundred years, and were widely imitated in other countries, especially Korea and Japan. Their demise came after they were overtaken in their markets by blue and white porcelain from Jingdezhen.

Goryeo Korea imitated Longquan celadon in glaze color, preserving its distinct green color. However, influenced by Liao Dynasty's own imitations of Longquan celadon, developed new shapes and patterns which led to the ultimately distinct bisaek celadon, which other countries (China, Japan, etc) considered “celebrated artworks.” The distinctive features of Goryeo's bisaek celadon include the green-gray hue and masterful incising abilities which added patterns to the ceramics’ surface.

In traditional Western terms, most celadons are strictly counted as stoneware, since the fired clay body is usually neither white nor translucent. In the traditional Chinese classification, which divides pottery into low-fired earthenware and high-fired porcelain, they count as porcelain. Compromise terms such as "porcellanous stoneware" may be used to describe the pieces, and some Western writers consider the wares should be "regarded as porcelains".

The Longquan celadons were among the finest of a range of celadon wares produced in China, and led stylistic and technical developments. The celadons were produced in a range of shades of colour, centred on olive-green, but extending to greenish blues (regarded as desirable, but less common) and browns. All these colours come from the glaze; the body beneath is sometimes left partly unglazed as part of the decoration, when it fires to a terracotta brown. The wares are hardly ever painted; decoration comes from the vessel shape and carved or incised designs in the body. Shapes were originally mostly simple, allowing the glaze colour to create the main effect of a piece, but in later periods raised decoration was common.

The body of Longquan celadon, as seen in fragments under glaze, varies from "a heavy, compact grey stoneware to an almost white porcellaneous material", but where fired at the surface this turns to a typical terracotta reddish brown, seen at the unglazed foot of many pieces, and when relief decoration is left unglazed (see below and illustration). This distinguishes Longquan from Northern Celadons. However, this may not be the case in pieces made from the most whitish, porcellanous, material, where the fired body may also "be translucent if thin enough". In Western sources, individual pieces are normally classified as stoneware, but some may be called porcelain; material translated from the Chinese is likely to describe all as "porcelain".

The body was normally thrown on the potter's wheel, with large vases often thrown in sections and luted together. Templates were used, and sometimes moulds, including two-part moulds, and moulds including decoration. Unglazed biscuit relief sections were achieved either by sprigging the reliefs over a glazed area before firing, where the surface would be flat in the kiln, or by adding a resist of wax or grease before glazing, when the sides of a vase were decorated.

The glaze colours vary across a wide spectrum of greyish to blueish greens, with some yellowish browns as well. The colour comes from iron oxide fired in a reducing atmosphere, and the colour varies with the temperature and the strength and timing of the reduction. Longquan celadon was fired in long dragon kilns, brick tunnels rising up a slope, with a series of chambers, and the best results came from the pots in the uppermost stages, which heated up more slowly and evenly. Saggars were always used, and the longer kilns, with up to twelve chambers, might have been able to fire as many as 25,000 pieces at a time. The firing temperature was probably between 1,180 °C and 1,280 °C, with the range over 1,250 °C giving the best green or blue colours. In some cases at least there appear to have been layers of glaze and also multiple firings to achieve a deeper glaze effect.