Frequency-swept lasers are used in many important applications, such as the high-precision optical spectrum analyzer, the high-resolution laser spectroscopy, the frequency-modulated continuous wave (FMCW) lidar, the optical frequency-domain imaging (OFDI), the optical time-domain reflectometry (OTDR) and the optical frequency-domain reflectometry (OFDR), the optical communications and microwave photonics, and fundamental scientific researches, as introduced in Sect. 7.1. The method of direct current modulation of LD is introduced in Sect. 7.2; the sweeping linearity and its characterization are discussed. Section 7.3 describes methods by using intra-cavity modulators and beam deflectors inside the ECDL cavity and the related electro-optic materials and devices. Section 7.4 introduces methods by using external modulations placed in the path out of laser cavity, and the related acousto-optic modulators and electro-optic modulators, especially the single side band modulator.