This paper deals with the aggegation behavior of microemulsion droplets, especially water droplets covered with a monomolecular surfactant layer in oil. In the first part a picture obtained by a number of experimental techniques reported in the literature is reviewed. In the second part we propose a model that describes the aggregation of microemulsion droplets into chainlike aggregates from a thermodynamic point of view. The model is shown to be capable of explaining experimental data measured in a ternary microemulsion using sodium bis(2-ethylhexyl)sulfosuccinate as surfactant quite well.