This paper discusses the evaluation of ductility in structures and structural assemblages through laboratory testing. Ductility is defined as the ability of a structure to undergo large amplitude cyclic deformations in the inelastic range without a substantial reduction in strength. The required ductility is determined through nonlinear time-history dynamic analysis or static mechanisms, while the available ductility is assessed experimentally. The paper outlines definitions for required and available ductility factors, including displacement, rotation, and curvature ductility factors. It also addresses the effect of hysteresis loop shapes on structural response and the importance of accurate definitions for yield and ultimate deformation. The paper recommends a quasi-static loading test procedure to determine the available ductility factor of a subassemblage. This procedure involves load-controlled and displacement-controlled test cycles, with the available ductility factor calculated based on the cumulative ductility factor at which the lateral load sustained has reduced to 80% of the maximum measured lateral load strength. The paper concludes that adequate ductility is essential in seismic design, and that experimental testing is crucial for determining the available ductility of structures. The recommended quasi-static loading test procedure provides a reliable method for assessing the ductility of structural subassemblages.This paper discusses the evaluation of ductility in structures and structural assemblages through laboratory testing. Ductility is defined as the ability of a structure to undergo large amplitude cyclic deformations in the inelastic range without a substantial reduction in strength. The required ductility is determined through nonlinear time-history dynamic analysis or static mechanisms, while the available ductility is assessed experimentally. The paper outlines definitions for required and available ductility factors, including displacement, rotation, and curvature ductility factors. It also addresses the effect of hysteresis loop shapes on structural response and the importance of accurate definitions for yield and ultimate deformation. The paper recommends a quasi-static loading test procedure to determine the available ductility factor of a subassemblage. This procedure involves load-controlled and displacement-controlled test cycles, with the available ductility factor calculated based on the cumulative ductility factor at which the lateral load sustained has reduced to 80% of the maximum measured lateral load strength. The paper concludes that adequate ductility is essential in seismic design, and that experimental testing is crucial for determining the available ductility of structures. The recommended quasi-static loading test procedure provides a reliable method for assessing the ductility of structural subassemblages.