In 2015, KASI has finished building a network of wide-field photometric survey systems called the Korea Microlensing Telescopes Network (KMTNet), which installed at three sites in the southern hemisphere (Chile, South Africa, and Australia). Each system consists of a 1.6m wide-field optical telescope equipped with a mosaic CCD camera of 18k by 18k pixels and it provides a 2.0 by 2.0 square degree field of view. The purpose of having three telescopes in three different time zones is to have 24-h uninterrupted monitoring of night sky sources in the southern hemisphere. The primary scientific goal of the KMTNet project is to discover extrasolar planets toward the Galactic bulge, and the main focus is on discovering Earth-mass planets in the habitable zone using gravitational microlensing. During the non-bulge season, the systems are used for wide-field photometric survey science on supernovae, asteroids, and external galaxies.