In this feature article, a phase diagram of a divalent surfactant is presented and discussed. The formation of the thermodynamically stable state of self-assembled supra-aggregates is demonstrated. Two different types of mesostructured fluids are described with either formation of a lamellar phase, containing and surrounded by a bicontinuous microemulsion, or interdigitated reverse micelles. These microstructures are used as templates where the control of the shape of copper nanocrystals is related to that of the microstructure. However, the template is not the only parameter which controls the shape of nanocrystals.