  Remote observing can be broadly defined as those observations where the
astronomer is not physically present at the telescope. Different
implementations presently in use include robotic telescopes, service observing
with or without eavesdropping and active remote observing. We briefly describe
the terminology, the pros and cons, the observing modes, and their
implementation at optical observatories.
  In the second part of the paper, we discuss the example of remote observing
with ESO's NTT. Different aspects of the technical setup and the support given
to observers, with emphasis on problems encountered, are described. With the
present system, we find that the observing efficiencies for local and remote
observing are identical: few projects still require local observations.
