The evolution of observing modes at ESO telescopes

From the implementation of Service Mode at the NTT in 1997 to the recent "designated" Visitor Mode observations, we review how the palette of observing modes and the types of programs have evolved at ESO. In more detail, we present how the evolution of tools at the disposal of external astronomers and the Observatory staff has enabled ESO to implement new types of observations. We also take a look at the new challenges posed by upcoming instruments at the VLT and present the first steps towards enabling remote observing for ESO telescopes.