Summary: This is a review of recent results on the disaggregation problem: given a collective demand function, is it or is it not the sum of individual demand functions, and, if it is, can one retrieve the individual demands from their given sum? There are several variants to this problem, depending on whether one deals with market demand or excess demand, but the general philosophy remains the same: to get interesting answers, i.e. to be able to discriminate between those collective demand functions which arise from individual utility maximization and those which do not, one needs microeconomic data (e.g., the individual allowances).