The Arp catalog is a collection of galaxies compiled by the American astronomer Halton Arp in 1966. It includes 338 peculiar galaxies, which are unusual in shape or structure, and aims to help astronomers study galaxy formation and evolution. Each entry in the catalog is accompanied by a photograph and a brief description. The catalog is particularly valuable for researchers interested in galactic interactions and mergers, as many of the listed galaxies exhibit signs of gravitational influence from nearby objects. The Arp catalog has become a key resource in the field of extragalactic astronomy.