  One of the main activities in high-energy and nuclear physics is the search
for the so-called quark-gluon plasma, a new state of matter which should have
existed a few microseconds after the Big Bang. A quark-gluon plasma consists of
free color charges, i.e. quarks and gluons, interacting by the strong (instead
of electromagnetic) force. Theoretical considerations predict that the critical
temperature for the phase transition from nuclear matter to a quark-gluon
plasma is about 150 - 200 MeV. In the laboratory such a temperature can be
reached in a so-called relativistic heavy-ion collision in accelerator
experiments. Using the color charge instead of the electric charge, the Coulomb
coupling parameter of such a system is of the order 10 - 30. Hence the
quark-gluon plasma is a strongly coupled, relativistic plasma, in which also
quantum effects are important. In the present work the experimental and
theoretical status of the quark-gluon plasma physics will be reviewed,
emphasizing the similarities and differences with usual plasma physics.
Furthermore, the mixed phase consisting of free quarks and gluons together with
hadrons (e.g. pions) will be discussed, which can be regarded as a complex
plasma due to the finite extent of the hadrons.
