A supercooled liquid is said to have a kinetic spinodal if a temperature Tsp exists below which the liquid relaxation time exceeds the crystal nucleation time. We revisit classical nucleation theory taking into account the viscoelastic response of the liquid to the formation of crystal nuclei and find that the kinetic spinodal is strongly influenced by elastic effects. We introduce a dimensionless parameter λ, which is essentially the ratio between the infinite frequency shear modulus and the enthalpy of fusion of the crystal. In systems where λ is larger than a critical value λc the metastability limit is totally suppressed, independently of the surface tension. On the other hand, if λ < λc a kinetic spinodal is present and the time needed to experimentally observe it scales as exp [ω/(λc−λ) 2 ], where ω is roughly the ratio between surface tension and enthalpy of fusion.When a liquid is cooled below its freezing point without forming a crystal, it enters a metastable equilibrium phase known as supercooled [1]. A supercooled liquid is squeezed in an uncomfortable time region: if we are too fast in measuring its properties, the system cannot thermalize and an off-equilibrium glass is formed; on the other hand, if we are too slow, the system has the time to nucleate the solid, and we obtain an off-equilibrium polycrystal, and, eventually, a thermodynamically stable crystal [2,3]. What is the maximum degree of supercooling a metastable equilibrium liquid can reach ?The tricky point about this question is that it mixes aspects of the experimental protocol, with intrinsic properties of the system. If we stick to cooling the system linearly in time, there is a minimum cooling velocity below which the system is bound to crystallize [3]. This velocity is inversely proportional to the minimum nucleation time as a function of temperature [4]: we cannot cool slower than this minimum cooling rate, otherwise crystallization occurs. On the other hand, as we cool, the relaxation time increases steeply, and therefore the system necessarily leaves the supercooled phase, and becomes a glass, at the temperature where the relaxation time becomes too large for this minimum cooling rate.To penetrate deeper in the supercooled region, one can use an ad hoc nonlinear cooling protocol: cool fast close to the temperature where crystallization is a concern [4], and where relaxation time is still small; and slow down at lower temperatures, to cope with the increasing relaxation time, once the nucleation time starts raising again. Therefore, we may think that the unique limitation to the extent of supercooling is given by our capability of cooling slow and fast enough a sample, and that in principle there is no bound to supercooling a metastable equilibrium liquid.In fact, our experimental capability is not the only limitation to supercooling a system. If at a certain temperature the relaxation time of the liquid τ R exceeds the nucleation time of the crystal τ N , no equilibrium measurements can be performed on the liquid sample and the ...