Diode lasers are very important in many research fields such as quantum precision measurement, quantum optics, atomic physics, etc. Traditional diode lasers usually use gratings and interference filters to adjust the output frequency, and the output frequency is finely mechanically adjusted to be near the atomic transition line, and then the laser frequency is locked by precision spectroscopy, such as saturated absorption spectroscopy, modulation transfer spectroscopy, etc. At the same time, Pound–Drever–Hall (PDH) technology is also often used for laser frequency locking and laser linewidth narrowing. When using precision spectroscopy technology to lock the laser frequency, the frequency of traditional diode lasers drifts or mutates in the case of long-term operation or changes in working parameters, causing the system to lose lock. However, the Faraday laser can keep the laser frequency continuously resonant with the atomic transition line during long-term operation when the driving current and working temperature of the laser diode fluctuate greatly, greatly improving the convenience and efficiency of the initial frequency locking and re-locking process after losing lock. This chapter considers the modulation transfer spectroscopy technology in precision spectroscopy locking as an example to show the process to achieve the locking of the Faraday laser frequency. At the same time, it demonstrates the process to lock the output frequency of the Faraday laser through PDH technology.