This chapter offers a comprehensive examination of the evolution of seismic design principles for concrete and steel building structures as outlined in US building codes, with a particular emphasis on the development and refinement of American Society of Civil Engineers (ASCE) 7 standards. The study traces the evolution of seismic design objectives and the parameters for seismic hazard ground motion specified in code provisions. It highlights the transition from Deterministic Seismic Hazard Analysis to Probabilistic Seismic Hazard Analysis, which has enabled a more nuanced assessment of seismic risks and ground motion probabilities. Key advancements discussed include the integration of site-specific hazard analyses, soil–structure interaction considerations, and the evolution of seismic force modification factors for steel and reinforced concrete seismic force-resisting systems to better account for ductility and overstrength. The chapter also addresses structural irregularities related to seismic design and the evolution of seismic detailing requirements for steel and reinforced concrete structures as specified in code provisions. Additionally, it explores advancements in seismic force calculations, including advanced dynamic analysis procedures such as Modal Response Spectrum Analysis and Nonlinear Time History Analysis, which have significantly enhanced the accuracy of predicting building performance under seismic loads. Furthermore, the adoption of risk-targeted seismic ground motion parameters and updated National Seismic Hazard Maps in recent ASCE 7 editions reflects a commitment to uniform collapse risk, ensuring consistent safety margins against seismic failure. This chapter aims to provide a thorough discussion of the background and development of seismic design principles, objectives, methodologies, and code provisions to aid structural engineers and practitioners in understanding the evolution of seismic design for reinforced concrete and steel structures in the United States.