  We review recent advances in the physics of strongly interacting charged
systems functioning in water at room temperature. We concentrate on the
phenomena which go beyond the framework of mean field theories, whether linear
Debye-Huckel or non-linear Poisson-Boltzmann. We place major emphasis on charge
inversion - a counterintuitive phenomenon in which a strongly charged particle,
called macroion, binds so many counterions that its net charge changes sign. We
discuss the universal theory of charge inversion based on the idea of a
strongly correlated liquid of adsorbed counterions, similar to a Wigner
crystal. This theory has a vast array of applications, particularly in biology
and chemistry; for example, the DNA double helix in the presence of positive
multivalent ions (e.g., polycations) acquires a net positive charge and drifts
as a positive particle in electric field. This simplifies DNA uptake by the
cell as needed for gene therapy, because the cell membrane is negatively
charged. We discuss also the analogies of charge inversion in other fields of
physics.
