This paper surveys recent approaches to the explanation of how the shape of mean demand is determined. The main focus is to address the following questions: Is it necessary to impose specific behavior of the households in order to achieve regularities of mean demand or is it sufficient to know that a certain degree of behavioral heterogeneity implies structural properties of mean demand, such as the Law of Demand? Firstly, results of classic, utility based, demand theory are presented. Secondly, newer approaches are shown which are essentially based on the fact that households behave heterogeneously. It is shown that both approaches may serve as a justification for structural properties of mean demand. (This version: March, 2002)
