Analysis and design of protection systems for highway bridges have witnessed extensive research activities in the last two decades. Researchers worldwide have studied highway bridges both analytically and experimentally and have documented the performances of highway bridges during recent earthquake events. Several damage mechanisms in both structural and geotechnical aspects of highway bridges have been recorded and analyzed in detail. Retrofit methods such as strengthening, base isolation, and other energy dissipative devices have been proposed, tested, and implemented in full-scale bridges. This special issue presents a spectrum of work from leading researchers highlighting the state of the art in the analysis, design, and protection of highway bridges. Estimation of seismic risk is a central element in earthquake engineering. Integral to this aspect are fragility curves, which relate the conditional probability of reaching or exceeding any damage state as a function of the hazard [e.g., peak ground acceleration (PGA)]. Estimation of seismic risk is then undertaken by combining the seismic hazard and fragility curves using the total probability theorem. Papers in this special issue range from the estimation of fragilities using incremental dynamic analysis to using fragility curves as a measure to evaluate the performance of seismic protection systems and soil-structure interaction effects. Tehrani and Mitchell, in the paper “Seismic Risk Assessment of Four-Span Bridges in Montreal Designed Using the Canadian Bridge Design Code,” assess the risk to 15 continuous four-span bridges in Montreal. All these bridges were designed according to the 2006 Canadian Highway Bridge Code and detailed with flexuredominated failures. By combining the seismic hazard to theMontreal region with the fragility curves for different limit states calculated using the incremental dynamic analysis, the authors conclude that the probability of exceeding these limit states is reasonably low. In the paper “Seismic Fragility Relationships of a Cable-Stayed Bridge Equipped with Response Modification Systems,” Barnawi andDyke present fragility curves developed using time-history analysis for a benchmark cable-stayed bridge subjected to 20 synthetic ground motions. The bridge was evaluated with various response modification systems, namely passive damper, an active control system, and a semiactive control system usingmagnetorheological (MR) dampers. Based on a comparison of their fragilities, the authors conclude thatMRdampers are an effective responsemodification strategy for cable-stayed bridges. Wang et al., in the paper “Influence of Soil-Structure Interaction and Liquefaction on the Isolation Efficiency of a Typical Multispan Continuous Steel Girder Bridge,” present results showing the effects of the soil-structure interaction and soil liquefaction on the fragility of base isolated and unisolated bridges. Using typical multispan continuous steel bridges from the central and southeastern United States as a test bed, they demonstrate that the soil-structure interaction and liquefaction adversely affects the efficiency of base isolation (although liquefaction provides some natural isolation). When highway bridges cross fault rupture zones, their dynamic behavior is considerably more complicated because of the incoherent groundmotions at their foundations. Saiidi et al., in the paper, “Shake Table Studies and Analysis of a Two-Span RC Bridge Model Subjected to a Fault Rupture,” study the effects of incoherent ground motions occurring when a bridge crosses a fault on the damage type and location of a two-span bridge using shake table tests. These tests, conducted at the University of Nevada, Reno, involved supporting three-column bents on three individual shake tables and commanding incoherent motions using this setup. They conclude that incoherent motions affect both the type and location of damage compared with coherent input. Furthermore, they conclude from their analysis using OpenSees that existing analytical models are capable of predicting experimental observations from their tests. Isolation systems are regarded as being extremely effective for protection of bridges during strong ground motions. It was possible to examine the performance of one such isolation system during the recent earthquake in Japan. The full-scale performance of a cablestayed bridge during the 2011 Tohuku earthquake is described by Siringoringo et al. in the paper “Seismic Response Analyses of the Yokohama Bay Cable-Stayed Bridge in the 2011 Great East Japan Earthquake.” This 860-m three-span steel truss double-deck bridge was densely instrumented (85 vibration sensors at 36 locations measuring displacements and accelerations) prior to the event, which allowed the authors to gain a rich body of information regarding its performance. The authors conclude that the link-bearing connection, which essentially isolates the bridge in the longitudinal direction, performed well and as intended. However, the relatively large transverse displacements of the tower and girders caused the existing gap distance to be exceeded, resulting in pounding. Nevertheless, the bridge did not sustain damage during the event, because the design hazard exceeded the actual event. In the paper “Novel Isolation Device for Protection of CableStayed Bridges against Near-Fault Earthquakes,” Ismail and Casas evaluate the performance of a roll-n-cage isolator that uses rolling to achieve isolation, gravity for recentering, and metallic yield dampers or damping. They present results on the Bill Emerson Memorial Bridge in Missouri, subjected to three near-fault ground motions. Their results demonstrate the effectiveness of this novel isolation system. Although isolation systems are ideal in many applications, lowcost alternatives to retrofit a large number of seismically deficient bridges in the midwestern United States are being investigated by infrastructure managers. Steelman et al., in the paper “Experimental Behavior of Steel FixedBearings and Implications for SeismicBridge Response,” present experimental results for a new concept being studied by the Illinois DOT. This is called the quasi-isolated case, wherefixed bearings in bridges are deliberately allowed to act as fuses during an earthquake and slide on the substructure, thereby limiting