Stora Alvaret is an alvar, a barren limestone terrace, in the southern half of the island of Öland, Sweden. Stora Alvaret is a dagger shaped expanse almost 40 kilometres (25 mi) long and about 10 kilometres (6 mi) at the widest north end. The area of this formation exceeds 260 square kilometres (100 sq mi), making it the largest such expanse in Europe and comprising over one fourth of the land area of the island.

Limestone is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of CaCO3. Limestone forms when these minerals precipitate out of water containing dissolved calcium. This can take place through both biological and nonbiological processes, though biological processes, such as the accumulation of corals and shells in the sea, have likely been more important for the last 540 million years. Limestone often contains fossils which provide scientists with information on ancient environments and on the evolution of life.