Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO3).

 Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera.

Limestone makes up about 10% of the total volume of all sedimentary rocks. The solubility of limestone in water and weak acid solutions leads to karst landscapes,in which water erodes the limestone over thousands to millions of years.  Most cave systems are through limestone bedrock.Limestone has numerous uses: as a building material,as aggregate for the base of roads, as white pigment or filler in products such as toothpaste or paints and as a chemical feedstock.

Limestone is very common in architecture, especially in Europe and North America. Many landmarks across the world, including the Great Pyramid and its associated complex in Giza,Egypt, are made of limestone. So many buildings in Kingston, Ontario, Canada were constructed from it that it is nicknamed the 'Limestone City’.

On the island of Malta, a variety of limestone called Globigerina limestone was, for a long time, the only building material available,and is still very frequently used on all types of buildings and sculptures. Limestone is readily available and relatively easy to cut into blocks or more elaborate carving.

 It is also long-lasting and stands up well to exposure. However, it is a very heavy material, making it impractical for tall buildings, and relatively expensive as a building material.

The Great Pyramid of Giza, one of the Seven Wonders of the Ancient World; its outside cover is made entirely from limestone.Courthouse built of limestone in Manhattan, Kansas.

 A limestone plate with a negative map of Moosburg in Bavaria is prepared for a lithography print.

Limestone was most popular in the late 19th and early 20th centuries. Train stations, banks and other structures from that era are normally made of limestone.

It is used as a facade on some skyscrapers, but only in thin plates for covering, rather than solid blocks. In the United States, Indiana, most notably the Bloomington area,has long been a source of high quality quarried limestone, called Indiana limestone. Many famous buildings in London are built from Portland limestone.

Limestone was also a very popular building block in the Middle Ages in the areas where it occurred, since it is hard, durable, and commonly occurs in easily accessible surface exposures.

Many medieval churches and castles in Europe are made of limestone. Beer stone was a popular kind of limestone for medieval buildings in southern England.

Limestone and (to a lesser extent) marble are reactive to acid solutions, making acid rain a significant problem to the preservation of artifacts made from this stone.

Many limestone statues and building surfaces have suffered severe damage due to acid rain. Acid-based cleaning chemicals can also etch limestone, which should only be cleaned with a neutral or mild alkalin-based cleaner.

Other uses include:

• It is the raw material for the manufacture of quicklime (calcium oxide), slaked lime (calcium hydroxide), cement and mortar. Pulverized limestone is used as a soil conditioner to neutralize acidic soils.
• It is crushed for use as aggregate—the solid base for many roads.
• Geological formations of limestone are among the best petroleum reservoirs;
• As a reagent in flue-gas desulfurization, it reacts with sulfur dioxide for air pollution control.
• Glass making, in some circumstances, uses limestone.
• It is added to toothpaste, paper, plastics, paint, tiles, and other materials as both white pigment and a cheap filler.It is added to toothpaste, paper, plastics, paint, tiles, and other materials as both white pigment and a cheap filler.
• It can suppress methane explosions in underground coal mines.
• Purified, it is added to bread and cereals as a source of calcium.
• Calcium levels in livestock feed are supplemented with it, such as for poultry (when ground up).
• It can be used for remineralizing and increasing the alkalinity of purified water to prevent pipe corrosion and to restore essential nutrient levels.
• Used in blast furnaces, limestone extracts iron from its ore.
• It is often found in medicines and cosmetics.
• It is used in sculptures because of its suitability for carving.