This article reviews hierarchical, comprehensive modeling techniques for millimeter-wave transistors that combine separate models for the semiconductor and the surrounding conductive elements. Physics-based and equivalent circuit-based models are presented for the active semiconductor, and full electromagnetic and equivalent circuit-based models are presented for the passive elements such as the electrodes and interconnects. At millimeter-wave frequencies, device dimensions approach the electromagnetic wavelength, and equivalent circuit-based models may become unsuitable. Under large signal operation, coupling between electromagnetic waves and charge carriers requires full-wave modeling techniques for accurate analysis as time-varying fields are significant compared to the DC bias fields with nonlinear wave-particle interactions. A mix of modeling techniques provides a reasonable balance of predictability and computational complexity.