This text covers both passive and active microwave circuits. The text provides detailed coverage of microwave tubes, solid state microwave amplifier design using scattering matrices, parametric amplifiers, and solid state oscillators and mixers. The author emphasizes modern applications of microstrip and other planar transmission lines for the realization of passive and active circuits. There is a systematic design strategy developed for microwave amplifiers that allows input and output voltage standing wave ratios, low noise, optimum gain and stability to be taken into account. The concept of impedance mismatch invariance is introduced to aid the design of multi-state amplifiers using unstable devices. This traditionally difficult topic is simplified by the design methods introduced in the text.