  We argue that the amazing progress of first-principles materials physics
necessitates a revision of the Standard Approach to electrodynamics of media.
We hence subject this Standard Approach to a thorough critique, which shows
both its inherent conceptual problems and its practical inapplicability to
modern ab initio calculations. We then go on to show that the common practice
in ab initio materials physics has overcome these difficulties by taking a
different, microscopic approach to electrodynamics of media, only superficially
resembling the Standard Approach whose validity is restricted to the
macroscopic domain. As this paradigm shift went largely unnoticed outside and
partly even within the ab initio community, the present article aims at a
systematic development and paradigmatic discussion of this new, microscopic
first-principles approach to electrodynamics of media, for which we propose the
name "Functional Approach".
