  We describe a real-space approach to the calculation of the properties of an
insulating crystal in an applied electric field, based on the iterative
determination of the Wannier functions (WF's) of the occupied bands. It has
been recently shown that a knowledge of the occupied WF's allows the
calculation of the spontaneous (zero-field) electronic polarization. Building
on these ideas, we describe a method for calculating the electronic
polarization and dielectric constants of a material in non-zero field. The
method is demonstrated for a one-dimensional tight-binding Hamiltonian.
