Formaldehyde (HCHO) is the simplest member of the class of organic compounds known as aldehydes. Aldehydes are distinguished by the presence and end position of a carbonyl group (-OH) attached to only one carbon atom. At room temperature, formaldehyde is an extremely reactive colorless gas with a suffocating odor. It is commonly sold as an aqueous solution (formalin) or in solid polymeric forms (paraformaldehyde and trioxane). Formaldehyde is used in the manufacture of dyes, in the production of synthetic resins, and in embalming and as a preservative for biological specimens.

Formaldehyde was first intentionally produced by August Hofmann, a German chemist (1818-1892), in 1867. Justus von Liebig had researched aldehydes earlier but had never succeeded in producing formaldehyde. Alexander Mikhailovich Butlerov (1828-1886) had hydrolyzed methylene acetate while trying to form methyl glycol and produced formaldehyde gas. He had noted that the product of the reaction behaved as an aldehyde. Hofmann, in 1867, exposed a mix of methyl alcohol vapors and air over a hot platinum spiral to form stable formaldehyde. Formaldehyde today is produced either from methanol, as Hofmann did, or by oxidizing hydrocarbons.

Due to health concerns, in 1992 the Occupational Safety and Health Administration (OSHA) lowered the legal exposure limits for formaldehyde from 1.0 parts per million to 0.75 parts per million. Nonetheless, the U.S. formaldehyde market remains strong with production anticipated to reach 12 billion lb (5.4 billion kg) annually by the end of the century.