The paper by Dominique Leguillon explores the criteria for crack onset at a notch, focusing on the interplay between energy and stress criteria. Both criteria are necessary conditions for fracture but neither is sufficient on its own. The energy criterion, based on the change in potential energy, and the stress criterion, based on the material's strength, are compared and contrasted. Experiments by Parvizi et al. on transverse cracking in cross-ply laminates provide evidence that the two criteria are complementary, with the energy criterion providing a lower bound for admissible crack lengths and the stress criterion providing an upper bound. The consistency between these two conditions forms a general criterion for crack nucleation, which coincides with the Griffith criterion for crack growth and the stress criterion for uniform traction along a straight edge. The paper derives a criterion for crack onset at a notch that combines both the toughness and strength of the material, ensuring that the two criteria hold true. This criterion is validated through comparisons with experimental results on homogeneous notched materials and bimaterial structures, showing good agreement. The paper also discusses the limitations of other approaches, such as Seweryn's formula, and provides a detailed analysis of the singular stress field around the notch tip.The paper by Dominique Leguillon explores the criteria for crack onset at a notch, focusing on the interplay between energy and stress criteria. Both criteria are necessary conditions for fracture but neither is sufficient on its own. The energy criterion, based on the change in potential energy, and the stress criterion, based on the material's strength, are compared and contrasted. Experiments by Parvizi et al. on transverse cracking in cross-ply laminates provide evidence that the two criteria are complementary, with the energy criterion providing a lower bound for admissible crack lengths and the stress criterion providing an upper bound. The consistency between these two conditions forms a general criterion for crack nucleation, which coincides with the Griffith criterion for crack growth and the stress criterion for uniform traction along a straight edge. The paper derives a criterion for crack onset at a notch that combines both the toughness and strength of the material, ensuring that the two criteria hold true. This criterion is validated through comparisons with experimental results on homogeneous notched materials and bimaterial structures, showing good agreement. The paper also discusses the limitations of other approaches, such as Seweryn's formula, and provides a detailed analysis of the singular stress field around the notch tip.