This work reports on electron spin resonance experiments in oriented single crystals of the hexagonal AlB 2 diboride compound (P6/mmm, D16h structure) which display conduction electron spin resonance.The X-band electron spin resonance spectra showed a metallic Dysonian resonance with g-value and intensity independent of temperature.The thermal broadening of the anisotropic electron spin resonance linewidth H tracks the T-dependence of the electrical resistivity below T 100 K.These results confirm the observation of a conduction electron spin resonance in AlB 2 and are discussed in comparison with other boride compounds.Based on our main findings for AlB 2 and the calculated electronic structure of similar layered honeycomb-like structures, we conclude that any array of covalent B-B layers potentially results in a conduction electron spin resonance signal.This observation may shed new light on the nature of the non-trivial conduction electron spin resonance-like signals of complex f-electron systems such as β-YbAlB 4 .