Gravitational Redshift of the CMB: The tiny temperature fluctuations in the Cosmic Microwave Background (CMB XIII.72) are affected by gravity. Photons climbing out of gravitational potential wells lose energy and are redshifted (gravitational redshift V.E.b, X.63), while those falling into wells are blueshifted. This "Integrated Sachs-Wolfe effect" (ISW) provides a test of GR and dark energy on cosmic scales.