Ancillary services ensure a proper operation of the power grid. The grid operators (transmission grid operators and distribution grid operators) are responsible for ancillary services. To ensure a reliable power supply, it is necessary that frequency, voltage, and power load remain within certain limits. This does not happen automatically, but through continuous corrections: namely, ancillary services. The most renowned service is probably the frequency control/balancing energy. Even in the event of a blackout, ancillary services help restart the power grid as quickly as possible. Ancillary services can be divided into four sections: Frequency measure, voltage measure, supply reconstruction, and operational management.