Cosmic rays exchange energy and momentum with their environments through kinetic scale plasma waves, affecting the dynamics, energy balance, and stability of the host systems on global scales. One of the most important consequences of cosmic ray – thermal gas coupling is its effect on the rate of star formation in galaxies, which is known as star formation feedback. Cosmic rays may also be implicated in regulating the activity of supermassive black holes in galactic nuclei, or AGN feedback. This article discusses the basic mechanisms by which cosmic rays feed back on their environments and places them in their astrophysical context.