Alzheimer's Disease is a tragic disease resulting in the gradual loss of memory and cognitive function and currently the most common dementing illness in the world with incidence (one's risk) doubling every 5 years. One of the key mysteries in the illness is the role of an endogenous protein, Amyloid-beta. Through clinical and experimental data, we have been able to develop a simple model to quantitatively describe the role of Amyloid-beta oligomers (transient higher-order structures) in Alzheimer's Disease. The model yields many results that are consistent with known data, such as how the risk rises among those with traumatic brain injuries, those with Down's Syndrome, and the exponential growth in risk with age. The model also makes predictions that could be later investigated experimentally.