- The only place where we can study collisionless shocks with in situ measurements is the heliosphere. Most high quality observations of the shock structure and charge particle acceleration have been done at the Earth bow shock. Extensive numerical simulations and theoretical research have been also aimed at the conditions typical for the bow shock, interplanetary shocks, and the termination shock. Much has become more clear due to the comparison of theory, simulations, and observations, but much is still has to be understood. Astrophysical shocks (like supernova remnant shocks, shocks in gamma-ray bursters, shocks in pulsar winds, etc.) cannot be observed directly. All we know about these shocks is deduced from observations of high energy particle radiation. Often conclusions about these shocks are made using direct extrapolation of what is known about heliospherical shocks to the expected extreme conditions in astrophysical objects (ultrarelativistic regimes, pair plasma). Such extrapolation is not always well grounded. On the other hand, some low energy restrictions of heliospherical shocks may be lifted up in relativistic shocks to increase the efficiency of particle acceleration. In particular, highly efficient electron energization at SNR and especially GRB shocks can be explained within the non-adiabatic shock crossing similar to what happens in thin quasi-perpendicular nonrelativistic shocks.