In chemistry, polycondensation refers to a type of reaction in which two molecules react with each other to form a larger molecule, with a smaller molecule such as water, alcohol, vinegar, ect. is released. Polycondensation reactions can occur in organic and inorganic chemistry and are used to produce polymers, resins, ceramics, metals, and other materials.

A well-known example of a polycondensation reaction is the production of polyester. This involves a reaction between a dicarboxylic acid tester and a diol, with water being released as a byproduct. The reaction results in the formation of a polyester polymer with a linear or branched structure that can be used to make textiles, films, coatings and other products.

Polycondensation reactions are often of great importance in materials science and can be used to produce polymers.