Modifications of gravity can leave an imprint on the cosmic microwave background radiation (CMB). This can either be due to new fifth forces mediated by a dark energy scalar field or new interactions coming from the time-evolution of dark energy or its spatial gradients. I will review how the CMB can be used to test modification of gravity. Both so-called conformal couplings and disformal couplings of a scalar field to other energy forms will be introduced and discussed.