The QCD Phase Diagram: Expectations and Challenges

A survey is given of recent QCD theory advances concerning the phase diagram, in particular the indications for a critical point and adjacent first order phase transition at high baryo-chemical potential, and the new ideas concerning a further phase at high μB, the quarkyonic matter phase. The latter state might finally explain the hadro-chemical equilibrium freeze-out points from A+A collisions at energies below SPS energy. We review several event-by-event fluctuation signals that promise to shed a light on the existence of a critical point, and we discuss its possible reflection in recent lattice QCD calculations.