Chemical cycling describes systems of repeated circulation of chemicals between other compounds, states and materials, and back to their original state, that occurs in space, and on many objects in space including the Earth. Active chemical cycling is known to occur in stars, many planets and natural satellites.

Chemical cycling plays a large role in sustaining planetary atmospheres, liquids and biological processes and can greatly influence weather and climate. Some chemical cycles release renewable energy, others may give rise to complex chemical reactions, organic compounds and prebiotic chemistry. On terrestrial bodies such as the Earth, chemical cycles involving the lithosphere are known as geochemical cycles. Ongoing geochemical cycles are one of the main attributes of geologically active worlds. A chemical cycle involving a biosphere is known as a biogeochemical cycle.

In most hydrogen-fusing stars, including the Sun, a chemical cycle involved in stellar nucleosynthesis occurs which is known as a carbon-nitrogen-oxygen or (CNO cycle). In addition to this cycle, stars also have a helium cycle. Various cycles involving gas and dust have been found to occur in galaxies.

The majority of known chemical cycles on Venus involve its dense atmosphere and compounds of carbon and sulphur, the most significant being a strong carbon dioxide cycle. The lack of a complete carbon cycle including a geochemical carbon cycle, for example, is thought to be a cause of its runaway greenhouse effect, due to the lack of a substantial carbon sink. Sulphur cycles including sulphur oxide cycles also occur, sulphur oxide in the upper atmosphere and results in the presence of sulfuric acid in turn returns to oxides through photolysis. Indications also suggest an ozone cycle on Venus similar to that of Earth's.

A number of different types of chemical cycles occur on Earth. Biogeochemical cycles play an important role in sustaining the biosphere. Notable active chemical cycles on Earth include:

Other chemical cycles include hydrogen peroxide.

Recent evidence suggests that similar chemical cycles to Earth's occur on a lesser scale on Mars, facilitated by the thin atmosphere, including carbon dioxide (and possibly carbon), water, sulphur, methane, oxygen, ozone, and nitrogen cycles. Many studies point to significantly more active chemical cycles on Mars in the past, however the faint young Sun paradox has proved problematic in determining chemical cycles involved in early climate models of the planet.

Jupiter, like all the gas giants, has an atmospheric methane cycle. Recent studies indicate a hydrological cycle of water-ammonia vastly different to the type operating on terrestrial planets like Earth and also a cycle of hydrogen sulfide.