This work is aimed at practitioners wishing to gain a broader systems-based perspective of phase-locked loops; and is also suitable as a graduate text for engineering students. It provides detailed coverage of digital sampling effects in modern phase-locked frequency synthesizers from a systems perspective, and discusses all aspects of phase noise, its mathematical modelling and its impact upon different digital communication systems. Sections on building blocks for frequency synthesis using phase-locked loops, frequency synthesis using sampled-data control systems, and MASCET, are included.