Molecular systems composed of peptides or proteins can be programmed to yield intriguing and potentially useful supra-molecular architectures. In the past decade peptide self-assemblies at interfaces have been the subject of various studies aiming at formation of molecular structures with predictable patterns and properties. Most of these systems utilized amphiphilic peptides, usually of a particular secondary structure, that self-assemble through non-covalent intermolecular interactions, into two-dimensional, organized supramolecular structures. The interest in design and preparation of self-assembled functional materials is driven by potential benefits to nanotechnology and nanobiotechnology. This review is restricted to amphiphilic peptide assemblies at interfaces studied by grazing incidence X-ray diffraction and atomic force microscopy, geared towards nanometer-scale structural characterizations.