The lipid membrane has been shown to mediate the fibrillogenesis and toxicity of Alzheimer's disease amyloid-β (Aβ) peptide. Electrostatic interactions between Aβ40 and the lipid headgroup has been found to control the association and insertion of monomeric Aβ into lipid monolayers, where Aβ exhibited enhanced interactions with charged lipids compared to zwitterionic lipids. To elucidate the molecular-scale structural details of Aβ-membrane association, we used complementary X-ray and neutron scattering techniques (grazing incidence X-ray diffraction, X-ray reflectivity, and neutron reflectivity) to investigate in situ the association of Aβ with lipid monolayers composed of either the anionic dipalmitoylphosphatidylglycerol (DPPG), zwitterionic dipalmitoylphosphatidylcholine (DPPC), or the cationic dipalmitoyltrimethyl-ammonium propane (DPTAP) lipid. We found that DPPG induced crystalline molecular ordering of Aβ at the membrane surface that closely mimicked the β-sheet spacing of Aβ in fibrils, revealing an intriguing templating effect of the anionic lipid DPPG on Aβ. Furthermore, incubating Aβ with lipid vesicles containing the anionic palmitoyloleoylphosphatidylglycerol (POPG) lipid accelerated the formation of amyloid fibrils, confirming that the templated ordering of Aβ seeded fibril formation. Our results implicate that the adsorption of Aβ to anionic lipids, which could become exposed to the outer membrane leaflet by cell injury, may serve as an in vivo mechanism of templated-aggregation and drive the pathogenesis of Alzheimer's disease.