The Control of Complex Systems Workshop brings together leading researchers in the control community, U.S. Department of Energy stakeholders, grid regulators, utility engineers, building scientists, and building controls and equipment vendors to discuss the technical obstacles and potential solutions to unlock the true potential of next generation power grids. This workshop is the third in the series, and first to be held as an ACC workshop. It emphasizes the interactions between the following technical areas as they relate to modernization of the electric power grid: 1) Dynamics and Control, 2) Analytics and Optimization, 3) Economics and Market Design. The workshop connects the research community with the real-world problems and specific technical challenges on the power grid transformation pathway towards highly integrated, maximally efficient, reliable, and secure operation. Control and decision-making applications relevant to all aspects of power grid operation are within scope, ranging from the bulk power system down to end point resources such as distributed renewable generation, energy storage systems, and residential and commercial buildings. The workshop is accessible by a broad controls audience, and it starts with tutorial sessions on the three technical areas. The tutorials will be particularly useful for beginning graduate students interested in working in the area of control for power systems. It then features both industry and academic research presentations discussing challenges and opportunities for applying advanced controls, analytics, and optimization to future power grids. The talks will provide a balance of theoretical and applied research.