In this poster we present a finite-field approach to compute density response functions, which allows for efficient GW and Bethe-Salpeter equation (BSE) calculations beyond the random phase approximation. The method does not require the explicit evaluation of dielectric matrices nor of virtual electronic states, and is easily applicable to density functional calculations performed with hybrid functionals. We present results for quasiparticle energies and exciton binding energies of molecules and solids, and absorption spectra of condensed systems of unprecedented size, including water and ice samples with hundreds of atoms.