Understanding how different proteins assemble into the ordered, insoluble aggregates associated with amyloid disease is a formidable challenge. Whilst it is generally accepted that protein misfolding is required for the formation of amyloid fibrils, the point at which the folding and aggregation free energy landscapes diverge, and the role of different amino acid residues in determining folding versus aggregation, remain obscure. Even more challenging is the identification of early aggregation-prone monomers and oligomeric species and their structural characterisation, since such species are aggregation-prone, short-lived and rapidly equilibrating. In this lecture I will describe how different biophysical methods are being used to reveal the mechanism by which normally soluble proteins convert into amyloidogenic conformations, how bimolecular collisions between protein variants can result in very different outcomes of assembly and how we have used small molecules to modulate the aggregation process.