The release of a dry-snow slab avalanche involves brittle fracture. It is therefore essentially a non-linear fracture mechanics problem. Traditional snow-stability evaluation has mainly focused on snow strength measurements. Fracture toughness describes how well a material can withstand failure. The fracture toughness of snow is therefore a key parameter to assess fracture propagation propensity, and hence snow slope stability. Fracture toughness in tension KIc and shear KIIc, was determined with notched cantilever-beam experiments in a cold laboratory. Measurements were performed at 3 different temperatures and with different snow types of density ƿ = 100-300 kg m-3 corresponding to typical dry-snow slab properties. The fracture toughness in tension KIc was found to be larger (by about a factor of 1.4) than in shear KIIc. Typical values of the fracture toughness were 500-1000 Pa m1/2 for the snow types tested. This suggests that snow is one of the most brittle materials known to man. A power-law relation of toughness KIc on relative density was found with an exponent of about 2. The fracture toughness in tension KIc decreased with increasing temperature following an Arrhenius relation below about -8°C with an apparent activation energy of about 0.16 eV. Above -6°C the fracture toughness increased with increasing temperature towards the melting point, i.e. the Atrhenius relation broke down. The key property in dry-snow slab avalanche release, the critical crack size under shear at failure, was estimated to be about 1 m.