Experimental studies of nucleus-nucleus collisions in the whole SPS energy range are reviewed. Selected topics such as statistical properties of the hadronic phase, strangeness production, fluctuations and correlations are discussed with regard to information on the onset of deconfinement and the critical point of strongly interacting matter. In spite of the very interesting results obtained in particular at the low SPS energies, additional data including rare probes such as charmed particles and di-leptons are required for a precise understanding of the underlying physics. An outlook about prospects and capabilities of upcoming experiments in this interesting energy region at RHIC, SPS, and in particular with CBM at FAIR, is given.