Density functional theory (DFT) rests upon the proofs by Hohenberg and Kohn, which show that all properties of quantum many-body systems are functionals of the ground state density, and the Kohn-Sham construction, in which the exchange-correlation energy is a functional only of the density. DFT has been widely assumed to apply directly to the intrinsic bulk properties of extended systems such as crystals, e.g., the static dielectric properties of insulators. However, in 1995, Godby, Ghosez, and Godby pointed out that the assumptions of DFT do not strictly apply to the case of a crystal in a finite electric field, since there is no ground state, and they argued that the description of intrinsic bulk dielectric phenomena in a crystal requires a functional of both the bulk density and the polarization. Here we discuss the results of recent work which show that in the limit of long wavelengths both the bulk (periodic) density and the bulk average macroscopic polarization are necessary to fully describe the dielectric properties of insulating materials.