Charged polyelectrolytes such as glycosaminoglycans are frequently found associated with the proteinaceous deposits in the tissues of patients with amyloid diseases. Experimental evidence indicates that they can play an active role in favoring amyloid fibril formation and stabilization. Binding of glycosaminoglycans to amyloid fibrils occurs prevalently through electrostatic interaction involving the negative polyelectrolyte charges with positively charged side chains residues. Similar to catalyzed reactions, glycosaminoglycans favor aggregation, nucleation and amyloid fibril formation functioning as a structural template for the self-assembly of highly cytotoxic oligomeric precursors rich in β-sheet into harmless mature amyloid fibrils. Moreover, the amyloid promoting activity of glycosaminoglycans can be facilitated through specific interactions via binding sites between amyloid polypeptide and glycosaminoglycan molecules. Numerous studies have identified common structural features in the heparin/heparin sulphate binding sites of proteins. Clusters of basic amino acid residues and consensus sequences consisting of alternating basic and non basic residues are capable to bind the negatively charged heparin as well as other glycosaminoglycan molecules in a variety of proteins that are induced to form β-structure upon interaction with the polyelectrolyte. Interestingly, heparin induces amyloid aggregation of globular proteins that do not exhibit any tendency to aggregate under physiological conditions. The well documented acceleration of fibril formation may open new strategies to limit the cytotoxicity of the early pre-fibrillar aggregates in patients suffering from amyloid diseases.