It has always been ESO's aim to operate the VLT in an interferometric
mode (VLTI) which allows the coherent combination of stellar light beams
col- lected by the four 8-m telescopes and by several smaller auxiliary
telescopes. In December 1993, in response to financial difficulties, the
ESO Council de- cided to postpone implement at ion of the VLTI, Coude
trains and associated adaptive optics for all the UTs but included
provisions for continuing tech- nological and development programmes
devoted to the aim of reintroducing these capabilities at the earliest
possible date. The desirability of carrying out the full VLTI programme
as originally envisaged at the earliest possible moment has not,
however, diminished, es- pecially in view of VLTI's exceptional
capabilities and resulting potential for new and exciting discoveries.
In recent years, interferometric projects have begun to playa central
role in ground-based high-resolution astronomy, and numerous instruments
have been completed or are in the process of construc- tion. Several
large-aperture interferometers will probably co me on-line near the turn
of the century. The impending presence of these new instruments
represents an important incentive both for clarifying the scientific
cases for various VLTI implementation plans and for ensuring VLTI's
competitiveness in the international context over the next 1O 20 years.