For electric power transmission overhead power line monitoring plays an important role in the operating security for grid operators, as well as for the supply availability at optimized cost under consideration of renewable energies. In this chapter, an approach for harvesting energy from the electric field around the power line to supply wireless sensor nodes is presented. High requirements for functionality, reliability and limited accessibility result in the development of a specific energy management strategy. The prototypes of the harvester and the power module were realized and tested under high-voltage (HV) laboratory conditions. A field test was carried out under real operating conditions. The test results confirm that the power module can collect enough energy to power the sensor nodes. The chapter presents theoretical considerations of energy availability from the electric field, the design of the energy harvester andmeasurements with the prototype in the HV laboratory and in the field. The field test results demonstrate that the energy harvested is enough to supply the sensor nodes at 16mW.