  The production of strange particles in a hot medium as produced in collisions
of heavy ions is considered one of the most important signals for the phase
transition to a quark-gluon plasma. In the first part of this lecture, the
theoretical description of strangeness production in hot matter is outlined for
a gas of quarks and gluons and for a hadronic gas and its impact on the
deconfinement phase transition. Then in the second part, constraints from the
underlying chiral symmetry of Quantum Chromodynamics (QCD) are utilized to
extract signals with strangeness for the chiral phase transition in hot matter.
