I present the results of large kinetic simulations of particle acceleration 
at non-relativistic collisionless shocks, which allow a first-principles 
investigation of cosmic ray (CR) acceleration at supernova remnants' shocks. 
Ion and electron acceleration efficiency and magnetic field amplification are 
investigated in detail as a function of shock inclination and strength, and 
compared with predictions of diffusive shock acceleration theory. 
Moreover, I outline an original mechanism (the "espresso mechanism") for the 
acceleration of nuclei up to 10^20eV in the relativistic jets of powerful 
active galactic nuclei. The combination of the supernova paradigm for the 
origin of Galactic CRs and the espresso mechanism provides a unified 
description of the global CR spectrum and chemical composition over more 
than 11 orders of magnitude in energy.