This book determines how to invest limited resources to increase the resilience of an infrastructure system against both non-deliberate and deliberate events. We propose an optimization model that seeks the best defensive investment for a weighted combination of deliberate and non-deliberate events. We formulate the general problem and conduct numerical analysis using a specific infrastructure system as a concrete example. We perform parametric analysis on the combined model in order to explore the way in which different solutions depend on the distributed weights and yield insight into the best investment decisions.