The article is an overview of our recent study on some particular aspects of polyelectrolyte complex (PEC) formation by oppositely charged polysaccharides when they are brought into contact in aqueous solutions. This type of complexation can lead to the thickening effect, jellification or PEC precipitation that find numerous applications in a variety of fields from the regulation of rheological characteristics of solutions to fabrication of functional materials by the layer-by-layer technique. Our focus was on the rheological aspects of water-soluble PEC formation and jellification, but to gain an insight into the mechanisms of the processes involved, atomic force microscopy, scanning electron microscopy and differential scanning calorimetry were also applied. As cationic polysaccharides, chitosan and cationic derivatives of hydroxypropylcellulose including hydrophobically modified samples were taken and, as their anionic counterparts, alginates, carrageenans, xanthans and fucoidans were used. Their combination allowed us to consider the influence of charge density, hydrophobicity and flexibility-stiffness of macromolecules on the association of oppositely charged polysaccharides, the formation of temperature sensitive hydrogels and some PEC morphological features. (C) Koninklijke Brill NV, Leiden, 2009