A plasma is matter in an ionized state. The assumption is often made that such matter is necessarily in a fluid state, and this is the case most often observed. However, cold, highly correlated ion plasmas confined in a vacuum by magnetic and electric fields have recently been observed to crystallize into lattice patterns that depend on the sizes and shapes of the plasmas. These studies are relevant to the understanding of dense astrophysical objects, such as neutron stars and white dwarfs, in which plasmas having similar properties are believed to exist.