A polyelectrolyte is a polymer with ionizable groups that dissociate in aqueous solutions, making the polymer charged. A polyelectrolyte is a polymer whose repeating units carry electrolyte groups. The properties of polyelectrolytes are therefore similar to those of electrolytes (salts) and polymers (high molecular weight compounds). Charged molecular chains, common in soft matter systems, play a fundamental role in determining the structure, stability and interactions of various molecular assemblies.