A condensation reaction (also known as a dehydration reaction) is a chemical reaction in which two molecules or moieties react with each other with the concurrent loss of water or ammonia. This type of reaction is used as a basis for the making of many important polymers for example: nylon, polyester and various epoxies. It is also the basis for the laboratory formation of silicates and polyphosphates. In biology, the formation of adenosine diphosphate and adenosine triphosphate from precursers and inorganic phosphate are also condensation reactions.
The reactions that form acid anhydrides from their constituent acids are typically condensation reactions.