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.
