Archetypical transport modes of CR fluids. Left: CRs tied to frozen-in magnetic fields are advected with the bulk plasma velocity, v_adv. Middle: when CRs are weakly scattered by Alfvén waves, they diffuse away from a given source (after an initial time) with an rms velocity of ﹩\sqrt{2\kappa /t}﹩ (where t is the time and κ denotes the diffusion coefficient) along the magnetic field. Right: if CRs are effectively scattered, they stream with the Alfvén speed, v_a, along the magnetic field.