Particle interferometry is a method to extract information on the
space-time characteristics of sources of particle emission.
The method is based on the quantum statistical (anti-)symmetry of the
wave-function of identical particles which encodes the space-time
information into the measurable two-body and many-body correlation functions.

Presently, particle interferometry provides a unique tool
to measure, on the fermi scale of $10^{-15}$ m, the volume of hot and
expanding systems at their freeze-out.  Since the total energy is well 
controlled, one may estimate the energy density reached with the help of 
the particle interferometry "microscope".  Thus one may infer whether the
Quark-Gluon Plasma, a new and long time desired state of the strongly 
interacting matter, has been formed (or not).  However, many non-ideal
 features of the two-particle correlations make the determination of the
underlying space-time picture highly non-trivial.

In the last 10 years it turned out that the interpretation of the data becomes
increasingly tricky if the source undergoes strong
 collective dynamics and has a short lifetime. A
multi-dimensional analysis of the 2-particle correlator as a function
of the relative and total momentum of the pairs is required to
separate geometric effects from dynamical ones. Many different model
calculations and numerical simulations of correlation functions
appeared on the market, and a concentrated experimental effort towards
a multidimensional investigation of the correlations in nuclear
collisions improved the quality and quantity of the data dramatically.

At the same time experimental efforts to systematically study 
multi-dimensional HBT interferometry in a large
kinematic domain and for various colliding systems from
proton-proton to Pb-Pb or Au-Au collisions at CERN SPS and BNL AGS energies
are providing extremely stringent tests for the model-builders
and showing evidence for unexpected, scaling behaviours in the data.

In summary the field is close to a transition point where
a new generation of data will be matched with a new generation of the
models. We expect that the tranditionally separated studies which
analyse the correlation functions and the invariant momentum distributions
independently will have to be merged to determine the model parameters 
uniquely.
 
We expext that an intense 2-week workshop can provide a unique opportunity 
for consolidation of ideas and methods as well as to identify the new 
challenges and the next levels of problems.

For this purpose, we plan to ask a few theoretically inclined experimentalists
to summarize the experimental status of particle interferometry
in the BNL AGS and CERN SPS heavy ion programme. These data provide the most 
detailed multi-dimensional analysis of the correlation function.
As a feature of the workshop  we plan to invite
experimetalists to organize the available data on both the correlation
functions and the invariant momentum distribution before the workshop
in such a manner that direct model comparisons, the testing of new ideas
and fitting expressions may become possible during the course of the workshop.

Although the main focus shall thus be on the above described hot topics
in high energy heavy ion physics, we would like to invite for review talks
some of the leading experts working with similar methods
in elementary particle physics, medium and low energy heavy ion physics
as well as in quantum optics. We expect that these invited
review talks will help us in understanding the non-ideal effects
and may possibely result in new applications of the methods and
techniques developed in various related fields.