In this chapter, the precision of optical clocks based on mode-locked laser (MLL) is compared with more conventional types of clock sources. It is shown that the phase noise of the optical pulse train from the MLL can be better than other types of clock sources by orders of magnitude. Then, an abstract representation of frequency synthesizer is demonstrated. Different techniques for RF generation using MLL are shown, and their pros and cons are discussed. Finally, a comparison of all these techniques is made with respect to their phase noise and capability to generate RF signal with different frequencies for different applications.