Improper protein folding (misfolding) can lead to the formation of disordered (amorphous) or ordered (amyloid fibril) aggregates. The major lens protein, a-crystallin, is a member of the small heatshock protein (sHsp) family of intracellularmolecular chaperone proteins that prevent protein aggregation. Whilst the chaperone activity of sHsps against amorphously aggregating proteins has been well studied, its action against fibril-forming proteins has received less attention despite the presence of sHsps in deposits found in fibril-associated diseases (e.g. Alzheimers and Parkinsons). In this review, the literature on the interaction of aB-crystallin and other sHsps with fibril-forming proteins is summarized. In particular, the ability of sHsps to prevent fibril formation, their mechanisms of action and the possible in vivo consequences of such associations are discussed. Finally, the fibril-forming propensity of the crystallin proteins and its implications for cataract formation are described along with the potential use of fibrillar crystallin proteins as bionanomaterials. ; H. Ecroyd and John A. Carver