Introducing the application of Field Effect Transistors (FET) as frequency multipliers and harmonic oscillators, this text puts emphasis on nonlinear techniques, and includes a minimal amount of mathematics and a combination of theory and experimentation. It aims to help microwave and millimeter-wave engineers comprehend the fundamental concepts and design rules of frequency multipliers and harmonic oscillators. The text focuses on the techniques required to generate harmonics and emphasizes hardware circuits. It explores the design of narrow and bandwidth doublers and triplers - both single-ended and balanced configuration. It also explains the association between oscillator theory and frequency multiplier theory in designing harmonic generators. The important issues when applying MIC or MMIC technologies are discussed to help designers decide on the best approach for a particular circuit.