Plasma constitutes more than 90% of the matter in the visible Universe. In typical space plasma systems, dissipation is provided via collective collisionless processes rather than through binary collisions between charged particles. Acceleration of charged particles to high energies is one of the most fundamental phenomena that occur in the universe and is also one of the major channels of the dissipation of the flow of energy. Collisionless Shocks (CSs) exist in almost every plasma environment observed either directly or indirectly such as: the Earth’s bow shock that forms the interface between the solar wind and the terrestrial magnetosphere, bow shocks in the vicinity of other planets, interplanetary shocks that separate different flows within the solar wind, at the boundaries of solar systems or heliospheres, around other stars, supernovae remnants, gamma-ray bursts, active galactic nuclei, and cluster of galaxies. CSs are found at all scales in the Universe: from only one centimetre in laboratory plasmas to megaparsec scales in galaxy clusters. CSs are, in many aspects, a unique plasma phenomenon. They are believed to be the most effective energizers of charged particles capable of accelerating particles to very high energies (up to ~10¹⁸ eV and probably even up to ~10²⁰ eV). A collisionless shocks is a multi-scale object where the interaction between the electromagnetic fields and charged particles provide the dissipation across all scales, starting with the electron inertial scale within the shock transition layer, and ending with the overall scale of the physical system. Physical processes at the whole multiplicity of the scales are interrelated. CSs are strongly nonlinear systems where the field-particle interactions are crucial. Understanding physics of CSs is not only necessary for knowledge of their outstanding role in the activity of plentitude of the known objects in the universe. This understanding is also relevant to the most fundamental phenomena in space plasmas such as acceleration, multi-scale processes, dissipation, and transition to irreversibility.