Protein and polysaccharide mixed systems have been actively studied for at least 50 years as they can be assembled into functional particles or gels. This article reviews the properties of electrostatic gels, a recently discovered particular case of associative protein–polysaccharide mixtures formed through associative electrostatic interaction under appropriate solution conditions (coupled gel). This review highlights the factors influencing gel formation such as protein–polysaccharide ratio, biopolymer structural characteristics, final pH, ionic strength and total solid concentration. For the first time, the functional properties of protein–polysaccharide coupled gels are presented and discussed in relationship to individual protein and polysaccharide hydrogels. One of their outstanding characteristics is their gel water retention. Up to 600 g of water per g of biopolymer may be retained in the electrostatic gel network compared to a protein gel (3–9 g of water per g of protein). Potential applications of the gels are proposed to enable the food and non-food industries to develop new functional products with desirable attributes or new interesting materials to incorporate bioactive molecules.