  I discuss two-particle intensity interferometry as a method to extract from
measured 1- and 2-particle momentum spectra information on the space-time
geometry and dynamics of the particle emitting source. Particular attention is
given to the rapid expansion and short lifetime of the sources created in
relativistic heavy-ion collisions. Model-independent expressions for the HBT
size parameters in terms of the space-time variances of the source are derived,
and a new parametrization of the correlation function is suggested which allows
to separate the transverse, longitudinal and temporal extension of the source
and to measure its transverse and longitudinal expansion velocity. The effects
of resonance decays are also discussed.
