Interpolyelectrolyte complexes (IPECs) are typically formed when two polyelectrolytes of opposite charge are mixed together in solution. We present an overview of different strategies for the preparation of micellar IPECs, i.e., structures where such IPEC domains form the core or the shell of micelles. In addition, vesicular architectures are considered, where the IPEC domain forms a membrane layer. One intriguing feature of IPECs is that their formation can be directed, their stability towards changes in pH or ionic strength can (to a certain extent) be predicted, and their size can be controlled. Especially the use of ionic/non-ionic block copolymers offers unique potential for the preparation of well-defined and sophisticated nanostructured materials. We also discuss possible applications, especially in the field of life sciences, including biocompatibility, the controlled uptake/release of guest substances, the immobilization of enzymes, or the controlled formation of inorganic/organic hybrid materials.