The energy system optimization problems are broadly categorized as operation and planning problems. The operation problems are usually related to how to exploit the existing devices/power plants. The planning problems usually refer to those problems which investigate whether to invest or not in some assets. The course Energy Systems Optimization introduces undergraduate and graduate students to applied optimization with a focus on energy systems. It includes the problem statement and mathematical formulation of a series of problems related to energy systems as well as their solution and results interpretation in commercial software packages. In particular, the subjects covered are:  Introduction to optimization in energy systems,  Basic optimization problems for gaining experience with the software package, thermal power units and renewable energy sources (static and dynamic formulation),  Long-term generation expansion planning of power systems,  Energy Storage,  Power flow analysis  Generation investment planning, and  Integrated Energy Systems.