Planetary Nebulae Populations in External Galaxies
  This review highlights the properties of the planetary nebulae in external galaxies as tracers of light, of the stellar population properties, and of the distances and kinematics of the parent galaxies. Recent results on the kinematics of the outer regions in giant elliptical galaxies and on the luminosity specific PN numbers (the \alpha\ parameter) in these systems are presented, based on current surveys of planetary nebulae with the Planetary Nebulae Spectrograph (PN.S) and other instruments. Finally a brief discussion is given of planetary nebulae as tracers of the diffuse light in the nearby clusters, such as Virgo and Hydra I. 
Magda Arnaboldi
astro-ph.CO