Experimental testing and analytical simulations have provided great opportunities in assessing the safety of structures in seismic regions. Experimental testing is a function of the size and number of the specimens, which hinders its application in the case of large structural systems such as medium-to-long span bridges and multistory buildings. On the other hand, analytical simulation is powerful but its inelastic response models are far from being accurate especially near structural collapse. Hybrid simulation for earthquake response assessment has been under development for over a decade, in response to the shortcomings of both testing and analysis. Experience and infrastructure now exist to design complex integrated experimental-analytical assessment environments for very large structures and their foundations by distributing the physical tests over any number of laboratories regardless of their geographical location, and to distribute the analysis over any number of computer programs, while maintaining all aspects of interaction between the components. This paper traces the recent history of hybrid simulation with specific reference to developments at the MUST-SIM Facility of the University of Illinois at Urbana-Champaign, USA. The concept is explained, and the integration software (termed UI-SIMCOR) is described. Several example applications are described. Amodel updating approach, which learns from the tested components to improve the analytical models during the test is explained. It is demonstrated that hybrid simulation is the most versatile and realistic platform for the assessment of structures and their foundations under earthquake loading up to structural collapse.