Generation and use of electrical energy in modern power grids with an increasing share of renewable energy requires power electronic converters as an interface for most of the components which are connected to the grid. This chapter deals with the fundamentals of power electronics for electrical drives, solar inverters, wind turbines, energy storage, and the production and use of hydrogen. It describes the structure and function of converters on the power grid, provides an introduction to operating behavior and characteristics of line- and self-commutated converters, and presents measurements of the line current and harmonic spectrum of some typical converter examples to provide a practical reference.