The mathematical model of the Giffen effect proposed in the article clearly demonstrates both the effect itself and the reasons for its manifestation. The main advantages of the model include its extreme simplicity, which opens up access to the widest circle of readers, the use of standard methods for solving the consumer choice problem, and the most important fundamental agreement with the results of the field experiment of Jensen and Miller. The model shows that any good for which there is a more expensive substitute can be of little value. This or that good is endowed with the appropriate property by a particular consumer due to his or her own preferences, income level and prevailing prices. Any good of little value, including those that can only be consumed by a high-income individual, may turn out to be Giffen’s goods. Therefore, the consumption of Giffen’s product cannot be considered as evidence of the low standard of living of the consumer. According to the model, an increase in demand for an increasingly expensive low-value good, which is the essence of the Giffen paradox, is the result of optimizing a set of goods, i.e. the result of rational consumer behavior. It is shown that for the manifestation of the Giffen effect, it is necessary that the amount of funds allocated by the consumer for the purchase of a low-value good and its more expensive substitute falls into a certain rather narrow range of values. The failures of numerous and long-term studies aimed at detecting empirical manifestations of Giffen behavior in various historical events are explained by the fact that the corresponding analysis was carried out on the basis of averaged rather than individual values of demand for all categories of consumers. As a result, the negative slope of the aggregate demand curve turned out to be dominant over the positive sections of certain individual demand curves.