Wear-protective hard transition metal nitride (TMN) thin films are distinguished by their superior thermal stability and oxidation resistance coupled with high Young¿s modulus and remarkable hardness. However, TMNs are inherently brittle materials with typically low toughness. This thesis introduces a multifaceted design approach comprising (i) a nanocomposite AlCrSiN microstructure and (ii) a multilayer architecture, which enables (iii) a controlled precipitation at grain boundaries within specific sublayers. The developed AlCrSiN multilayer film exhibits an extrinsic toughening mechanism, leading to a significant enhancement of fracture resistance. In this study, two reference monolithic thin films, namely Al0.63Cr0.27Si0.1N and Al0.675Cr0.075Si0.25N, along with a multilayer thin film, containing alternating sublayers of the two reference materials, were deposited using cathodic arc evaporation. Additionally, a carefully adjusted vacuum heat-treatment at 1050°C for 5 min was applied in order to tailor the microstructure through precipitation. Correlative nanoscale characterization through (i) scanning electron microscopy, (ii) transmission electron microscopy and (iii) cross-sectional synchrotron X-ray nanodiffraction revealed a nanocomposite microstructure composed of wurtzite Al(Cr)N and cubic Cr(Al)N nanocrystals with sizes of about 5 nm. Heat-treatment led to the precipitation of cubic Cr(Al)N in the thin film material with lower Si content, Al0.63Cr0.27Si0.1N, whereas the Al0.675Cr0.075Si0.25N thin film material remained unaffected by the heat treatment. In the multilayer sample, this led to the alternating occurrence of sublayers with abundant precipitation and sublayers devoid of any precipitation. Mechanical properties were assessed by performing in situ micromechanical tests on freestanding cantilevers fabricated by focused ion beam milling. Unnotched and notched cantilevers were loaded to fracture in order to determine Young¿s modulus, fracture stress and fracture toughness, respectively. The in-situ observed stepwise crack propagation revealed an unprecedented extrinsic toughening mechanism, which resulted in the significant improvement of the fracture response. In summary, the correlative analysis of the carefully-designed cross-sectional microstructure and mechanical properties of the AlCrSiN thin films paved the way for the development of a new generation of wear-protective hard thin films with improved fracture behaviour.