  In this review we cover the detection, identification and astrophysical
importance of planetary nebulae (PN). The legacy of the historic Perek &
Kohoutek and Acker et al. catalogues is briefly covered before highlighting the
more recent but significant progress in PN discoveries in our Galaxy and the
Magellanic Clouds. We place particular emphasis on the major MASH and the IPHAS
catalogues, which, over the last decade alone, have essentially doubled
Galactic and LMC PN numbers. We then discuss the increasing role and importance
that multi-wavelength data is playing in both the detection of candidate PN and
the elimination of PN mimics that have seriously biased previous PN
compilations. The prospects for future surveys and current efforts and
prospects for PN detections in external galaxies are briefly discussed due to
their value both as cosmic distance indicators and as kinematical probes of
galaxies and dark matter properties.
