TiAlN coatings deposited by vapor deposition techniques have been used for many years for cutting applications due to their thermal stability and hardness, enabling them to withstand tribological demands. The age hardening of the ternary system due to spinodal decomposition and the effect of a fourth alloying element have been studied thoroughly in the last decades. In the present thesis, the effect of Ta alloying on the microstructure, mechanical properties and thermal stability of TiAlN hard coatings with a constant Ti/Al atomic ratio of 50/50 was investigated for coatings synthesized using cathodic arc evaporation. Powder metallurgically prepared targets with a Ta content increasing from 0 % to 15 % were used. During the deposition process, the bias voltage was gradually increased. After annealing in a vacuum furnace, the microstructure and mechanical properties were investigated using X-ray diffraction and nanoindentation, respectively. Additionally, differential scanning calorimetry was performed on powdered coatings to detect microstructural changes during the heating process. Furthermore, the deposition process was altered for selected coatings by changing the applied bias voltage to investigate its influence on the thermal stability of samples within the TiAlTaN system. In summary, it has been shown that alloying with Ta improves the thermal stability of coatings within the TiAlN system by retarding the decomposition of the supersaturated solid solution into its stable constituents cubic TiN and wurtzite AlN. Therefore, the hardness of coatings after vacuum annealing up to 1000 °C increases with increasing Ta content. The high temperature properties can be further improved by adjusting the bias voltage during the deposition process, resulting in decomposition at higher temperatures and consequently, in enhanced mechanical properties up to higher temperatures.