  We review the progress in understanding the strange particle yields in
nuclear collisions and their role in signalling quark-gluon plasma formation.
We report on new insights into the formation mechanisms of strange particles
during ultrarelativistic heavy-ion collisions and discuss interesting new
details of the strangeness phase diagram. In the main part of the review we
show how the measured (multi-)strange particle abundances can be used as a
testing ground for chemical equilibration in nuclear collisions, and how the
results of such an analysis lead to important constraints on the collision
dynamics and space-time evolution of high energy heavy-ion reactions.
