Abstract. The dynamics of a driven interface in a medium with random pinning forces is analyzed. The interface undergoes a depinning transition where the order parameter is the interface velocity v, which increases as v N ( F -F,)' for driving forces F close to its threshold value F,. We consider a Langevin-type Eq. which is expected to be valid close to the depinning transition of an interface in a statistically isotropic medium. By a functional renormalization group scheme the critical expo- Here, we present details of the perturbative calculation and of the derivation of the functional flow Eq. for the random-force correlator. The fixed point function of the correlator has a cusp singularity which is related to a finite value of the threshold F,, similar to the mean field theory. We also present extensive numerical simulations and compare them with our analytical results for the critical exponents. For E = I the numerical and analytical results deviate from each other by only a few percent. The deviations in lower dimensions E = 2,3 are larger and suggest that the roughness exponent is somewhat larger than the value [ = ~/ 3 of an interface in thermal equilibrium.