How can we explore the onset of deconfinement by experiment?

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.