Wind and solar energy have seen significant decreases in the cost of these technologies over that last decade which has lead to increasing levels integrated into the grid. They also offer unique benefits such as no fuel costs, quick installation, and no pollution. But as more variable renewable energy (VRE) such as wind and solar is integrated into electrical power systems, a range of new technical challenges is becoming more prevalent in planning and operating the grid. Challenges include dealing with variable and uncertain power production as well as the unique physical characteristics that wind and solar generators have. This special section looks at some of the new techniques to solve these challenges with integrating ultra-high levels of VRE.