This project investigates the seismic behavior and vulnerability of reinforced concrete (RC) buildings with irregular stiffness configurations, both with and without shear walls. The primary objectives are to study the effect of vertical geometric irregularity on the performance level of structures subjected to seismic loading, and to evaluate the influence of shear walls in mitigating seismic vulnerabilities. Three G + 15 RC frame building models are analyzed: a regular frame, an irregular frame with stiffness irregularity, and an irregular frame with stiffness irregularity incorporating shear walls. Detailed numerical simulations and seismic hazard analyses are conducted for all three models, considering a high seismic zone V scenario. Nonlinear static pushover analyses are performed to assess the inelastic behavior, identify potential failure mechanisms, and compare key parameters such as shear forces, bending moments, story drifts, and node displacements. The seismic performance and stability of the structures are evaluated based on these parameters. The results reveal significant differences in the seismic response of regular and irregular RC frames, particularly in terms of story drifts, displacements, and the distribution of internal forces. The presence of shear walls is shown to substantially enhance the lateral stiffness and overall seismic performance of the irregular structures, reducing drift demands, improving global stability, and mitigating the effects of stiffness irregularities. The findings highlight the importance of considering vertical irregularities in the design of RC buildings and the potential benefits of incorporating shear walls to mitigate seismic vulnerabilities, especially in regions with high seismic hazard. The conclusions provide valuable insights for structural engineers and decision-makers in earthquake-prone areas.