Transition metal diboride (TMB) coating materials are the subject of growing research interests. They are considered potential candidates in future industrial applications ranging from thermo-mechanical purposes in UHT environments to electrochemical needs. Exploring the phase space of novel TMBs poses specific challenges: (i) susceptible compositional and structural variety during physical vapor deposition (PVD), (ii) anisotropy in their mechanical properties as well as brittle nature, and (iii) formation of non-adherent and volatile oxide scales. Within this talk, we want to address these specific challenges on a step-wise alloying concept from binary to quaternary group IV to VI transition metal diborides. The anisotropic nature and impact of B-rich tissue phases on the intrinsic fracture toughness of superhard binary TiB2±z and WB2±z are elaborated as a starting point. Subsequently, different alloying routes (e.g. TM-X-B2±z, TM-X-Si-B2±z) will be discussed to enhance the ductile character and oxidation resistance. Here, Si and disilicide alloying routes have been proven highly effective in providing long-term oxidation resistance up to 1200 °C (e.g. < 350 nm oxide scale after 10 h). To describe all these relations comprehensively, we correlated the synthesis parameters with structural and morphological evolution using XRD, HR-TEM, APT, ERDA, and micro-mechanical testing methods.