Numerous studies have concluded that the interaction of the amyloid β-peptide (Aβ) and cellular membranes contributes to the toxicity and cell death observed in the progression of Alzheimer's disease. Aggregated Aβ species disrupt membranes, leading to physical instability and ion leakage. Further, the presence of Aβ on the membrane surface increases the aggregation rate of the peptide, as diffusion occurs in two dimensions, increasing the probability of interpeptide interactions. Molecular dynamics (MD) simulations have been used to investigate Aβ in a number of environments, including aqueous solution and membranes. We previously showed that monomeric Aβ40 remains embedded in membranes composed of the most common lipids found in the cell membrane, but that the presence of ganglioside GM1 promotes release of the peptide into the extracellular medium. Here, we explore the interactions of two Aβ40 peptides in model membranes to understand whether aggregation can occur prior to the release of the peptide into the aqueous environment. We found that aggregation occurred, to different extents, in each of the model membranes and that the aggregates, once formed, did not exit the membrane environment. This information may have important implications for understanding the affinity of Aβ for membranes and the mechanism of Aβ toxicity in Alzheimer's disease.