  Optical observations of the companions of pulsars can help determine the
properties of the binaries, as well as those of their components, and give
clues to the preceding evolution. In this review, we first describe the
different classes of binary pulsars, and present a table with a summary what is
known about their optical counterparts. Next, we focus on the class of pulsars
that have low-mass, helium-core white dwarf companions. We discuss attempts to
determine the masses of both components using optical spectroscopy, and compare
the pulsar spin-down ages with cooling ages of the white dwarfs. We confirm
that for a given age, the lowest-mass white dwarfs are much hotter than the
more massive ones, consistent with recent evolutionary models, although with
one glaring exception. We discuss the case of PSR B0820+02, where the cooling
age indicates a braking index less than 3, and conclude by describing how
cooling ages can be used to test formation scenarios for PSR J1911-5958A, a
pulsar binary in the outskirts of NGC 6752.
