Nucleus--nucleus collisions provide the unique opportunity to create and to investigate dense nuclear matter in the laboratory. The collision experiments address fundamental aspects of strong-interaction physics: the nuclear equation-of-state at high baryon densities, and the modification of hadron properties in the dense nuclear medium. The experimental results are relevant for our understanding of the dynamics of core-collapse supernovae, and of the structure of neutron stars. In particular, strange particles are promising diagnostic probes of dense nuclear matter. Existing experimental data, their theoretical interpretations, and future experiments will be discussed.

PACS numbers: 25.75.Dw