Recent years have seen increases in the number of data breaches. This chapter attempts to quantify the impacts of data breaches in terms of the monetary costs incurred by providers and consumers. This is important because data breaches are a major factor when allocating funds for security controls. Case studies involving the Equifax incident in 2017 and the Target incident in 2013 are employed to demonstrate that the cost impacts of data breaches are significant for providers as well as consumers. The cost components in the overall cost function for providers and consumers are presented. Guided by open-source data, the cost components in the provider portion of the cost function are expressed as best-fit functions of time since the data breach. An important point in the cost quantification is that equal weights are assigned to the costs incurred by the provider and the consumers.