Many techniques have been developed to aid in the purchase of an information system, especially human resource information systems. Analysis shows that these techniques are all predicated on basic psychological decision making theories. Reviewing these psychological decision models helps explain the true intent of the various techniques: to keep the decision maker at as rational and optimal a process as possible. Understanding the psychological models will aid those considering an information system, no matter which technique they choose to follow. Knowledge of the models can also give additional direction when a chosen technique encounters situations beyond its purview.