Many physical infrastructure systems in the built environment, as well as facilities and utilities (transportation, water, power, and telecommunications) are complex adaptive systems with emergent systemic behaviour patterns that result from dynamic interactions among their inter-related components. Infrastructure systems can be viewed as a structured network of interdependent mechanisms that enable service delivery capability of physical assets, predominantly inherent to infrastructure. Infrastructure interdependencies in effect means a bi-directional relationship between multiple different infrastructures in a 'system of systems' through which the state of each infrastructure influences, or is influenced by, the state of another. This paper considers research into infrastructure systems interdependencies with regard to vulnerability risks induced by natural, technological and intentional hazards. The vulnerability of infrastructure, and infrastructure systems, is their exposure and sensitivity to potential impacting changes or hazards that affect their adaptive capacity. Infrastructure and most infrastructure systems have a designed adaptive capacity or resilience to impacting status changes or hazards. Such an adaptive capacity represents the capability and scope in being able to modify the infrastructure to increase its capacity to cope with change impacts or natural hazards, either in the short-term (such as with severe climate conditions), or in the long-term (such as with progressive climate change). The long-term adaptive capacity of infrastructure systems to impacting changes or hazards is viewed as the sustainable adaptive capacity of infrastructure and infrastructure systems-or simply, its sustainability. The complexity and interconnectedness of infrastructure systems raises research challenges in the modelling and analysis of such impacting status changes or hazards. A broad systemic assessment of the vulnerability, risk exposure, and adaptive capacity of infrastructure systems is thus required, which is ideally suited to systems dynamic modelling.