Introduction to Complex System Resilience -- Optimal Control Approach to Identifying Cascading Failures -- Jacobian-free Newton-Krylov Method for Risk Identification -- Security Monitoring using Converse Lyapunov Function -- Online Gaussian Process Learning for Security Assessment -- Risk Identification of Cascading Process under Protection -- Model Predictive Approach to Preventing Cascading Process -- Robust Optimization Approach to Uncertain Cascading Process -- Cooperative Control Methods for Relieving System Stress -- Distributed Optimization Approach to System Protection -- Reinforcement Learning Approach to System Recovery -- Summary and Future Work.