Polymerization is a chemical reaction in which monomers (small molecules) combine to form a larger, more complex molecule called a polymer. This process can occur through different mechanisms such as addition or condensation reactions and involves the breaking of covalent bonds between monomer units and the formation of new covalent bonds in the resulting polymer chain. Polymers are widely used in various industries, including plastics, textiles, and materials science due to their unique properties such as strength, flexibility, and resistance to environmental factors.