The interactions between metal ions and water-soluble polymers (WSP) have gained great interest due to their intrinsic properties as well as their potential applications, such as superconducting materials, ultra-high strength materials, liquid crystals, and biocompatible polymers. This review attempts to provide a general coverage of various scientific aspects of the WSP–metal ion interactions in aqueous solution and their applications. It includes fundamental aspects on synthesis of water-soluble polymers, as well as different activities and properties. A particular emphasis is given to the study the WSP–metal ion interactions, under different experimental procedures, through the liquid-phase polymer based retention (LPR) technique, which combines the use of WSP and membrane ultrafiltration. Theoretical work on this WSP–metal ion interaction has been elaborated to explain the counterion binding to polyelectrolytes, and the polymer–metal ion complex formation.