Many of the known planets – in the solar system Mars and beyond – will survive the post main-sequence evolution of their host stars into white dwarfs. Later interactions scatter asteroids, moons, and possibly entire planets deep into the gravitational potential of the white dwarf, where they are disrupted by tidal forces. Observational evidence for such evolved planetary systems is ubiquitous in the form of photospheric contamination by planetary material, circumstellar discs, and transits. The study of white dwarfs accreting planetary debris provides insight into the  bulk compositions of exo-planets conditions, the efficiency of planet formation around A/F type stars, and the architectures of outer planetary systems inaccessible to direct detections.