The exact factorization of the time-dependent electron-nuclear wavefunction is a formalism introduced in 2010 by Gross and coworkers to express a molecular wavefunction as the product of a marginal nuclear and a conditional electronic amplitude. This formalism is a generalization to the time domain of the analogous static factorization developed by Hunter and adopted later on in other groups , and has found until today many different applications for the interpretation and the simulation of electron-nuclear dynamics beyond the Born-Oppenheimer approximation.