Most of the arc volume is electrically neutral except for thin anode and cathode layers where strong electric fields are present. These typically collision-less layers have voltage drops of about 10 – 20 V. Ions, which are produced within the cathode layer, accelerate in this voltage and impact the cathode surface with high energies. This process heats the cathode stimulating thermal electron emission, which sustains the high discharge currents. On the cathode surface the electric currents concentrate at fast moving spots with sizes of 1 – 100 μm. Within these spots, the cathode material reaches local temperatures of 3000 C, leading to its evaporation and a slow cathode erosion. Pulsed atmospheric arc technology improves the arc stability at low electric currents, maximizes the discharge volume, and together with it the production of reactive species for plasma activation, while at the same time reducing the size of the driving high voltage electronics. These factors make it economically very attractive for industrial applications. There are two ways of using electric arcs for surface activation: non-transferred and transferred electric arcs. In the non-transferred technique, both electrodes are part of the plasma source. One of them also acts as a gas nozzle producing a stream of plasma. After the plasma stream leaves the arc region, the ions recombine quickly, leaving the hot gas having high concentrations of chemically active hydrogen, nitrogen and oxygen atoms and compounds, which is also called remote plasma. The temperature of this gas stream is of the order of 200 – 500 C. The gas is very reactive allowing high surface treatment speeds when only a short-time contact with the substrate is sufficient to achieve the activation effect. This gas can activate all materials, including temperature-sensitive plastics. Moreover, it is electrically neutral and free from electric potentials, which is important for activation of sensitive electronics. In the transferred technique of using the electric arcs, the substrate itself plays the role of the cathode. In this case, the substrate is subject not only to the reactive chemical species, but also to their ions with energies of up to 10 – 20 eV, to high temperatures reaching within the cathode spots 3.000 C, and to UV light. These additional factors lead to even greater activation speeds. This treatment method is suitable for conductive substrates such as metals. It reduces metal oxides by their reactions with hydrogen species and leaves the surface free from organic contaminants. Moreover, the fast moving multiple cathode spots create a microstructure on the substrate improving mechanical binding of the adhesive. Corona discharges appear at atmospheric pressures in strongly non-uniform electric fields.