An overview of some important results is presented in measurement of optical fibers by interferometric methods in two domains. Both time-domain and spectral-domain measurements are analyzed theoretically including the effect of the first-order and second-order intermodal dispersion. In the time-domain measurements, a tandem configuration of a Michelson interferometer and a few-mode optical fiber is used and the spatial interference fringes are resolved to measure the intermodal group optical path difference. In the spectral-domain measurements, the intermodal interference at the output of an optical fiber alone shows up as a periodic modulation of the source spectrum when a high-resolution spectrometer is used. Utilizing a white-light spectral interferometric method employing a low-resolution spectrometer and a tandem configuration of a Michelson interferometer and an optical fiber under test, the equalization wavelengths are resolved and the intermodal dispersion in the optical fiber can be measured over a wide spectral range. We have used the method for measuring either intermodal dispersion in circular-core, elliptical-core and bow-tie fibers or dispersion of birefringence in elliptical-core fibers.