  We describe the fundamental equations for description of electron-photon
interactions in insulating nanostructures. Since the theory for the
nanostructures are based on the theory for the bulk crystals, we shall describe
elements of the theory for the bulk crystals \cite{knox}-\cite{b2} in the first
three subsections. It is important in discussions on optical phenomena that
both the envelope function and the Wannier functions (or, equivalently,
cell-periodic parts of the Bloch functions) should be taken into account. The
theory for the nanostructure is discussed in the fourth subsection. In the
final subsection, we briefly mention quantum optics in nanostructures.
