Amyloidosis is a disorder of protein folding in which normally soluble proteins are deposited in the interstitial space as insoluble and remarkably stable fibrils that progressively disrupt tissue structure and function of organs throughout the body. Protein misfolding and aggregation have increasingly been recognized in the pathogenesis of various other diseases, but amyloidosis—the disease directly caused by extracellular amyloid deposition—is a precise term with critical implications for patients with a specific group of life-threatening disorders. Amyloidosis may be acquired or hereditary and the pattern of organ involvement varies within and between types, though clinical phenotypes overlap greatly. Virtually any tissue other than the brain may be directly involved. Although histology remains the diagnostic gold standard, developments in scintigraphy and MRI technology often produce pathognomonic findings. Systemic amyloidosis is usually fatal, but the prognosis has improved as the result of increasingly effective treatments for many of the conditions that underlie it, notably the use of biologic anti-inflammatory agents in patients with AA amyloidosis and new immunomodulatory agents in patients with AL type. Better supportive care, including dialysis and solid organ transplantation, have also influenced the prognosis favourably. A range of specific novel therapies are currently in clinical development, including RNA inhibitors that suppress production of amyloid precursor proteins, drugs that promote their normal soluble conformation in the plasma, and immunotherapy approaches that directly target the amyloid deposits.