ven if particularly elusive and indifferent to anything at ordinary energies, neutrinos have assuredly influenced the formation of the large-scale structure of the universe. In precision cosmology, modeling it carefully is necessary. In the linear regime, a satisfying description exists. It is the Boltzmann method. Unfortunately, extending it analytically to the nonlinear regime is particularly challenging. In this talk, I will present an alternative to this approach. It consists in a relativistic generalization of the formalism used to describe cold dark matter beyond the linear regime.