Engineered and natural environments are exposed to adverse operating conditions during their life-cycle, with deterioration and hazards posing a constant threat to their reliability and resilience. Optimal decision-making for such systems is concerned with controlling the extent and consequences of this exposure through scheduling of efficient strategies, from preventive planning to post-disaster recovery, with the objective to minimize the involved socioeconomic and environmental risks. To be successful in this objective, decision optimization needs to holistically alleviate multi-faceted complexities arising, among others, by the curse of dimensionality related to large-scale multi-component systems; the curse of history related to long-term sequential decisions; the model and data uncertainties; the operational constraints; the presence of multiple agents and decision layers;  and, finally, the sheer connection of physics-based engineering models with the optimization process. This line of research studies solutions to the above challenges through novel conceptual and computational frameworks within the contexts of stochastic optimization, systems reliability & control, and artificial intelligence.