The paper discusses the definitions and methods for evaluating ductility in structures and structural assemblies, particularly in the context of seismic design. It covers the required and available ductility factors, methods for estimating yield deformation and maximum available deformation, and experimental testing procedures. The author emphasizes the importance of ensuring that the available ductility is at least equal to the required ductility to ensure structural performance during severe earthquakes. The paper also reviews different types of experimental testing methods, such as shake table testing, pseudodynamic testing, and quasi-static cyclic load testing, and provides a recommended quasi-static loading test procedure to establish the available ductility factor for a subassemblage. The conclusion highlights the need for consistent definitions and testing procedures to ensure proper assessment and comparison of structural performance in seismic design.The paper discusses the definitions and methods for evaluating ductility in structures and structural assemblies, particularly in the context of seismic design. It covers the required and available ductility factors, methods for estimating yield deformation and maximum available deformation, and experimental testing procedures. The author emphasizes the importance of ensuring that the available ductility is at least equal to the required ductility to ensure structural performance during severe earthquakes. The paper also reviews different types of experimental testing methods, such as shake table testing, pseudodynamic testing, and quasi-static cyclic load testing, and provides a recommended quasi-static loading test procedure to establish the available ductility factor for a subassemblage. The conclusion highlights the need for consistent definitions and testing procedures to ensure proper assessment and comparison of structural performance in seismic design.