Glycosaminoglycans (GAGs) have been known since the 1980s to co-localize with amyloid deposits, yet many questions remain unanswered with regard to their interactions with amyloid. This chapter focuses on the molecular and biophysical aspects of these interactions. The interactions between GAGs and protein are believed to be mainly electrostatic in nature, involving GAG sulfate moieties which are proposed to bind the basic amino acids in a stoichiometric fashion, leaving the mature complex electrically neutral. It remains unclear whether GAGs protect the cell from toxic oligomers formed prior to the mature fibrils or rather increase the formation of aggregated species, leading to increased toxicity. Besides accelerating fibrillation in amyloidogenic proteins, GAGs have also been found to induce amyloid formation in non-amyloidogenic proteins as a possible storage-and-release switch. Thus, GAG-amyloid interactions may be both beneficial and pathologic. Clearly, there is scope for more research to address these intriguing molecular aspects.