Studies in the field of laser science and technology have resulted in the creation of a unique passively mode-locked laser generating a continuous regular train of ultrashort pulses. The unique feature of this laser is that it combines the properties of a radiation source with the output spectrum consisting of numerous extremely narrow strictly equidistant spectral lines with the properties of a radiation source emitting ultrashort high-power laser pulses. This feature has permitted a wide range of remarkable results. The basic properties of continuous-wave passively mode-locked lasers are discussed and their main applications are considered.