Coal is a fossil residue of dead plant material. This organic material was deposited in peat bogs, where plant material accumulated over long periods of time and formed so-called peat deposits.

Through a variety of biochemical and geochemical processes, the formerly loose peat is transformed into solid coal over long periods of time. Over the years, the biogenic source material is converted according to the coalification series via peat, lignite and coal to anthracite.

The largest deposits and resources of hard coal (sub-bituminous coal, bituminous coal and anthracite) were formed mainly during the Carboniferous, Permian and Jurassic periods of the Earth's history. Lignite comes primarily from the Tertiary period worldwide.

The largest coal-producing countries in recent years have been Australia, the Russian Federation, China, India, Indonesia, Kazakhstan, South Africa and the United States. With a share of over 50% of global coal production, China is currently by far the most important coal-producing country in the world.

Lignite is mined in three areas (called mining districts) in Germany. These include the Rhenish mining district west of Cologne, the Central German mining district in the Leipzig area, and the Lusatian mining district near and south of Cottbus.

The last two German hard coal mines in the Ruhr and Ibbenbüren areas ceased production at the end of 2018. Until 2012, hard coal was also mined in the Saar area and, until 1997, in the Aachen-Erkelenz area.

In addition to its primary use in electricity generation, coal also has other relevant applications in the heating market, coal gasification and liquefaction, and coke making. In particular, coke produced from coking coalcannot yet be fully replaced in the production of pig iron in the steel industry.