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Hydrocarbons are chemical compounds composed exclusively of carbon and hydrogen atoms. They represent the largest and most diverse class of organic molecules and form the core of many natural and industrial materials, including fuels, lubricants, solvents, and the raw materials for plastics and other chemicals. Hydrocarbons occur naturally in fossil fuels such as natural gas and crude oil, and they also arise in biological systems and through synthetic processes in industry.

Chemically, hydrocarbons are classified into aliphatic hydrocarbons (alkanes, alkenes, and alkynes) and aromatic hydrocarbons. Aliphatic hydrocarbons include saturated alkanes, with the general formula CnH2n+2, and unsaturated alkenes (CnH2n) and alkynes (CnH2n-2). Aromatic hydrocarbons contain ring structures with delocalized electrons, the most well-known example being benzene, C6H6. The distinct bonding and structural patterns give hydrocarbons a wide range of physical properties and reactivities.

Occurrence and production are linked to geology and industry. In nature, hydrocarbons accumulate in fossil fuels formed over millions of years. Industrially, they are produced, refined, and transformed through processes such as cracking, reforming, and polymerization to yield fuels and chemical feedstocks.

Uses and environmental considerations: hydrocarbons serve as fuels for transportation and heating, and as feedstocks for plastics, solvents, and many chemicals. Combustion releases carbon dioxide and water; incomplete combustion can emit carbon monoxide, soot, and other pollutants. Their extraction and use are major factors in energy policy, climate change, air quality, and land and water management.