  Although there is abundant and diverse observational evidence in support of
white dwarf stars hosting planets or debris disks which form in the
catastrophic destruction of various planetary bodies, the key processes that
explain these observations are still being intensely investigated. The study of
white dwarf planetary systems offers a unique perspective on exo-solar
composition, that cannot be obtained by any other means. This chapter describes
the various observational techniques that are used in order to find and
characterize exo-planets and debris disks around white dwarfs. In turn, it
discusses how to theoretically interpret these observations by surveying an
array of various research tools and models currently employed in this field.
