Cosmic ray acceleration at relativistic and ultrarelativistic shock waves

Using the Monte Carlo simulations we apply a method of discrete small amplitude particle momentum scattering to reproduce highly anisotropic conditions at relativistic shocks. We discusse acceleration times scales in relativistic shocks. Next, we describe newly found acceleration mechanism at ultrarelativistic shocks. The universal spectral index and the acceleration time for the shocks are given. In the end reflections from ultrarelativistic shocks are considered.