  There is little doubt that Quantumchromodynamics (QCD) is the theory which
describes strong interaction physics. Lattice gauge simulations of QCD predict
that in the $\mu,T$ plane there is a line where a transition from confined
hadronic matter to deconfined quarks takes place. The transition is either a
cross over (at low $\mu$) or of first order (at high $\mu$). It is the goal of
the present and future heavy ion experiment at RHIC and FAIR to study this
phase transition at different locations in the $\mu,T$ plane and to explore the
properties of the deconfined phase. It is the purpose of this contribution to
discuss some of the observables which are considered as useful for this
purpose.
