A survey of theoretical and experimental results on plasmas with strong Coulomb interactions is given. First the basic theoretical concepts describing nonideality, degeneracy and screening are introduced. The general structure of the thermodynamic functions and the phase diagram in the density - temperature plane is explained. Relevant experiments including shock waves and pulse-produced plasmas are briefly reviewed. Results on the critical data, thermodynamic and electric properties around the critical point and in supercritical states are discussed. The existence of high-pressure, high-temperature plasma phase transitions is investigated. After a brief discussion of transport properties the kinetics of ionization and reaction processes is studied. The influence of nonideality on ionization and nuclear fusion rates is investigated.