Limestone is a sedimentary rock, mainly composed of mineral calcite. The primary source of the calcite is usually marine organisms, which settle out of the water column and are deposited on the ocean floors as pelagic ooze (but see lysocline for information on calcite dissolution). Secondary calcite may also be deposited in super-saturated meteoric waters, as is evidenced by the creation of stalagmites and stalactites.

Bands of limestone emerge from the Earth's surface in often spectacular rocky outcrops and islands. For example the Verdon Gorge in France, Malham Cove in North Yorkshire, England and the Ha Long Bay National Park in Vietnam.

Limestone consists of sedimentary rock wholly or in large part composed of calcium carbonate. It is ordinarily white but may be coloured by impurities, iron oxide making it brown, yellow, or red and carbon making it blue, black, or gray. The texture varies from coarse to fine. Most limestones are formed by the deposition and consolidation of the skeletons of marine invertebrates; a few originate in chemical precipitation from solution. Limestone deposits are frequently of great thickness.

Limestone often tends to be more expensive than Marble, Travertine and Granite, it also tends to be very popular with many discerning Architects, Designers, Builders, and Consumers.

More and More interior décor publications are emphasising on the use of Limestone and Travertine not only as a wise investment long-term to ceramics and terracotta but for the ease of maintenance and overall appearance.

It is quarried for roadbeds and gravel roads, building and landscape construction, and cement manufacture.