This paper proposes a new mechanics-based model for the seismic design of beam-to-column panel zone joints in steel moment-resisting frames. The model is based on realistic shear stress distributions retrieved from continuum finite element (CFE) analyses of representative panel zone geometries. Comparisons with a comprehensive experimental data set suggest that the proposed model predicts the panel zone stiffness and shear strength with a noteworthy accuracy, even in panel zones featuring columns with thick flanges (thicker than 40 mm), as well as in cases with high beam-to-column aspect ratios (larger than 1.5). In that respect, the proposed model addresses the limitations of all other available models in the literature. If doubler plates are deemed necessary in the panel zone design, the CFE simulations do not depict any doubler-to-column web shear stress incompatibility, provided the current detailing practice is respected. Hence, the total thickness of the column web and doubler plates should be directly used in the proposed panel zone model. The panel zone shear strength reduction due to the axial load effects should be based on the peak axial compressive load, including the transient component due to dynamic overturning effects in exterior joints. It is found that the commonly used von Mises criterion suffices to adequately predict the shear strength reduction in the panel zone. (C) 2021 American Society of Civil Engineers.