In this contribution, nonlinear synthesis techniques for microwave circuits are presented. Emphasis is made on their principles, implementation, and applications. Four main types of nonlinear circuit are considered: frequency mixers, oscillators, frequency dividers and frequency multipliers. The operation principles and their main characteristics are introduced, together with the most useful synthesis techniques. Approximate analytic techniques like Volterrra series and the describing funciton are presented, as well as design tools, based on harmonic balance, such as the auxiliary generator, for oscillator and frequency multipliers. Analyses of noise and stability are also carried out. The techniques are illustrated by means of simple but practical FET‐based circuits.