This paper describes the supramolecular assembly of a macrocyclic beta-sheet containing residues 16-22 of the beta-amyloid peptide, A beta X-ray crystallography reveals that the macrocyclic beta-sheet assembles to form double-walled nanotubes, with an inner diameter of 7 nm and outer diameter of 11 rim. The inner wall is composed of an extended network of hydrogen-bonded dimers. The outer wall is composed of a separate extended network of beta-barrel-like tetramers. These large peptide nanotubes pack into a hexagonal lattice that resembles a honeycomb. The complexity and size of the peptide nanotubes rivals some of the largest tubular biomolecular assemblies, such as GroEL and microtubules. These observations demonstrate that small amyloidogenic sequences can be used to build large nanostructures.