The ‘magic frequency’ protocol has made it possible to design new type of atomic clocks based on well-engineered perturbations. Such ‘optical lattice clocks’ will allow extremely precise and speedy timekeeping, which targets fractional uncertainty of 10^-18, by using a large number of atoms and by sharing ‘magic frequency’ protocol. This paper covers motivations for developing such clocks and their experimental realizations. Possible impacts and future applications of optical lattice clocks are discussed, such as testing the fundamental laws of physics and developing relativistic geodesy.