Phase stability and mechanical properties of multimetal-boronnitride (Hf,Ta,Ti,V,Zr)-B-N are investigated by computational and experimental methods. Ab-initio calculations of (Hf,Ta,Ti,V,Zr)-B-N with different B:N ratios show a strong preference for the fcc NaCl-type structure over other structures (including the hcp AlB2-type) up to a B:N ratio of 3.5. Reactive deposition of (Hf,Ta,Ti,V,Zr)-B-N thin films leads to the formation of fcc solid solution + X-ray-amorphous BN with a corresponding decrease in hardness from 32.5 (no B) to 16.7 GPa (18 at% B). Non-reactively sputtered (Hf,Ta,Ti,V,Zr)-B-N coatings are single-phase fcc solid solutions, up to the maximum B:N ratio of 1.12. All non-reactively sputtered multimetal-boronnitride coatings contain a high Zr metal-fraction and ~8 at% C. The single-phase coatings reach superhardness up to 46.3 GPa. Even after vacuum annealing to 1200 °C, the hardness of the coating with a B:N ratio of 1.03 is still 43.7 GPa, while that of ZrN0.72C0.28 decreased from 36.3 to 30.2 GPa. Our results demonstrate the importance of the deposition technique to allow for the formation of a single-phase fcc-(Hf,Ta,Ti,V,Zr)-B-N with exceptional properties.