To provide a copolymer which can impart sufficient dynamic water repellency, after air-drying water repellency and friction durability to a surface of an article, and which has low impact on the environment, a method for producing the same, a water repellent composition and an article excellent in dynamic water repellency, after air-drying water repellency and friction durability. A copolymer which is characterized in that it has structural units based on the following monomer (a) and structural units based on the following monomer (b), wherein the content of structural units based on the monomer (a) is from 5 to 95 mass % in the total structural units (100 mass %), the content of structural units based on the monomer (b) is from 5 to 60 mass % in the total structural units (100 mass %) and the sum of the contents of structural units based on the monomer (a) and structural units based on the monomer (b) is at least 65 mass % in the total structural units (100 mass %), and a water repellent composition which comprises the copolymer: Monomer (a): a (meth)acrylate having no Rf group and having a C20-30 alkyl group; Monomer (b): a halogenated olefin.