Colloidal plasmas may "condense'' under certain conditions into liquid and
crystalline states, while retaining their essential plasma properties. This
"plasma condensation'' therefore leads to new states of matter: "liquid pl
asmas'' and "plasma crystals.'' The experimental discovery was first report
ed in 1994, and since then many researchers have begun to investigate the p
roperties of condensed plasma states. In this paper we describe some of the
basic physics required to understand colloidal plasmas and discuss experim
ents conducted to investigate the details of the interaction between the pl
asma particles (in particular, the interaction potential!, the melting phas
e transition, and the thermodynamics of this new state of matter. (C) 1999
American Institute of Physics. [S1070-664X(99)91105-9].