Drywall (also called plasterboard, dry lining, wallboard, sheet rock, gib board, gypsum board, buster board, turtles board, slap board, custard board, gypsum panel and gyprock) is a panel made of calcium sulfate dihydrate (gypsum), with or without additives, typically extruded between thick sheets of facer and backer paper, used in the construction of interior walls and ceilings. The plaster is mixed with fiber (typically paper, glass wool, or a combination of these materials); plasticizer, foaming agent; and additives that can reduce mildew, flammability, and water absorption.

In the mid-20th century, drywall construction became prevalent in North America as a time- and labor-saving alternative to lath and plaster.

Sackett Board was invented in 1890 by New York Coal Tar Chemical Company employees Augustine Sackett and Fred L. Kane, graduates of Rensselaer Polytechnic Institute.^{[citation needed]} It was made by layering plaster within four plies of wool felt paper. Sheets were 36 by 36 by 1⁄4 inch (914 mm × 914 mm × 6 mm) thick with open (untaped) edges.

Gypsum board evolved between 1910 and 1930, beginning with wrapped board edges and the elimination of the two inner layers of felt paper in favor of paper-based facings. In 1910 United States Gypsum Corporation bought Sackett Plaster Board Company and by 1917 introduced Sheetrock. Providing installation efficiency, it was developed additionally as a measure of fire resistance. Later air entrainment technology made boards lighter and less brittle, and joint treatment materials and systems also evolved. Gypsum lath was an early substrate for plaster. An alternative to traditional wood or metal lath was a panel made up of compressed gypsum plaster board that was sometimes grooved or punched with holes to allow wet plaster to key into its surface. As it evolved, it was faced with paper impregnated with gypsum crystals that bonded with the applied facing layer of plaster. In 1936, US Gypsum trademarked ROCKLATH for their gypsum lath product.

In 2002, the European Commission imposed fines totaling €420 million on the companies Lafarge, BPB, Knauf and Gyproc Benelux, which had operated a cartel on the market which affected 80% of consumers in France, the UK, Germany and the Benelux countries.

A wallboard panel consists of a layer of gypsum plaster sandwiched between two layers of paper. The raw gypsum, CaSO₄·2H₂O, is heated to drive off the water and then slightly rehydrated to produce the hemihydrate of calcium sulfate (CaSO
₄·⁠1/2⁠H
₂O). The plaster is mixed with fiber (typically paper and/or glass fiber), plasticizer, foaming agent, finely ground gypsum crystal as an accelerator, EDTA, starch or other chelate as a retarder, and various additives that may increase mildew and fire resistance, lower water absorption (wax emulsion or silanes), reduce creep (tartaric or boric acid). The board is then formed by sandwiching a core of the wet mixture between two sheets of heavy paper or fiberglass mats. When the core sets, it is dried in a large drying chamber, and the sandwich becomes rigid and strong enough for use as a building material.

Drying chambers typically use natural gas today. To dry 1,000 square feet (93 m²) of wallboard, between 1,750,000 and 2,490,000 BTU (1.85–2.63 GJ) is required. Organic dispersants and plasticizers are used so that the slurry will flow during manufacture and to reduce the water and hence the drying time. Coal-fired power stations include devices called scrubbers to remove sulfur from their exhaust emissions. The sulfur is absorbed by powdered limestone in a process called flue-gas desulfurization (FGD), which produces several new substances. One is called "FGD gypsum". This is commonly used in drywall construction in the United States and elsewhere.

In 2020, 8.4 billion square meters of drywall were sold around the world.