Narrow-linewidth external cavity diode lasers (ECDLs) have the advantages of compact structure, tunable wavelength, and low noise. They are widely used in quantum precision measurement, optical communication, laser radar, and other fields. In this article, four types of narrow linewidth ECDL using different frequency selection devices are introduced, including grating-ECDL, interference filtering ECDL, waveguide-ECDL, and Faraday laser. The article presents the basic structure and frequency selection mechanism, advantages and disadvantages of the ECDLs, as well as their international research progress. The first three types of ECDLs use non-quantum devices for frequency selection, while Faraday lasers utilize the resonant Faraday optical rotation effect for frequency selection. Therefore, the output wavelength corresponds to the atomic transition line directly and has good robustness against the fluctuations of the diode temperature and current as well. Then, the applications of these ECDLs are introduced, especially their typical applications in precision measurement. Finally, the future development of narrow linewidth ECDL is summarized and prospected.