With the combined impact of concerns about energy usage and environmental deterioration, integrated energy systems (IESs) are acknowledged to be a promising approach to increasing the efficiency of energy utilization by exploiting complementary (alternative) energy sources and storages. IESs show favorable performance for improving the penetration of renewable energy sources (RESs) and accelerating the low-carbon transition. However, as more renewables penetrate the energy system, their highly uncertain characteristics challenge the system scheduling and operation with significant impacts on safety and economic issues. To this end, this book will provide systematic method to address the aggravating uncertainties in IESs from two aspects: distributionally robust optimization and online operation.