Significance One histologic hallmark of Alzheimer’s disease is the self-assembly of amyloid β peptide (Aβ) into insoluble amyloid aggregates. This aggregation process is strongly dependent on environmental conditions and metal ions, such as zinc, have been shown to modulate Aβ aggregation. To understand the underlying molecular mechanism of how zinc affects fibril formation we analyzed the aggregation kinetics and could conclude that zinc causes a significant reduction in elongation rate (i.e., monomer addition to the fibril ends). We used NMR methods to elucidate the details of zinc binding and we found that the N terminus of Aβ transiently folds around the zinc ion, forming a metastable dynamic complex.