Shocks are ubiquitous in astrophysical environments with wide ranges of plasma parameters: the Earth’s bow shock, supernova remnants, shocks induced in relativistic jets, and ICM shocks driven by mergers of galaxy clusters. Furthermore, they come in different flavors: from non-relativistic to relativistic, from parallel to perpendicular, from subcritical to supercritical, from weak to strong shocks, and so forth. These shocks are known to produce cosmic ray (CR) particles via diffusive shock acceleration (aka Fermi first order process), which can be observed through their nonthermal emission in the EM spectrum from radio to gamma-ray. The first part of my talk will review broadly the kinetic plasma processes relevant to CR injection in collisionless shocks. Then, a variety of high energy astrophysics problems involving the CR acceleration will be discussed in the second part.