The amyloid-β(Aβ ) cascade hypothesis of Alzheimers disease (AD) has dominated research and subsequent therapeutic drug development for over two decades. Central to this hypothesis is the observation that Aβ is elevated in AD patients and that the disease is ultimately characterized by the central deposition of insoluble senile plaques. More recent evidence, however, suggests that the presence or absence of plaque is insufficient to fully account for the deleterious role of elevated Aβ in AD. Such studies support the basis for an alternate interpretation of the Aβ cascade hypothesis. Namely, that soluble oligomers of Aβ (i.e., ADDLs) accumulate and cause functional deficits prior to overt neuronal cell death or plaque deposition. Accordingly, the following review focuses on research describing the preparation and functional activity of ADDLs in vitro and in vivo. These studies provide the basis for an alternate, ADDL-based, view of the Aβ cascade hypothesis and accounts for the disconnect between plaque burden and cognitive deficits. Possible therapeutic approaches aimed at lowering ADDLs in AD patients are also considered.