Ionic polymers are present almost everywhere in the world, biological systems being the most important reservoir of ionic polymers such as nucleic acids, and many proteins, alginic acid and so on. Artificial ionic polymers derived from natural polymers such as chitin, cellulose or starch, by adequate chemical transformations, and a multitude of synthetic ionic polymers are generated in the laboratory. They can contain ionic or ionisable groups. Ionic polymers, either artificial or synthetic, have a multitude of applications such as: stabilisation or destabilisation of dispersions, thickening of solutions, oil recovery aids, water purification, corrosion inhibitors, soil conditioners, anti-static agents, additives in cosmetics and foods, surface modification, and so forth. Solid ionic hybrid materials found applications such as polymer electrolytes or substrates for the organic synthesis in solid phase. Many books and article reviews were dedicated to this wide class of polymers but the permanent diversification of their structures and applications ask for new and updated overviews on this field. Therefore, this book reports updated information from literature as well as original contributions in the field of ionic (co)polymers and hybrids, mainly on the applications of ionic polymers and hybrids such as: self-assembled multi-layers, ionic polymers containing azobenzene chromophore, phase separation processes, chelating ion exchangers, polymer electrolytes, functionalised solid surfaces and ionic hybrid hydrogels.