In this paper, the concept of a hybrid substructure for offshore wind turbines (OWT) is presented. Within the nationally funded research project “HyConCast - Hybrid Substructure of High Strength Concrete and Ductile Iron Castings”, the design concept of the substructure and its relevant design criteria have already been defined. The innovative design consists of large, thin-walled ductile cast iron joints connecting high-strength, lightweight precast concrete pipes. The most relevant design objective is to make optimal use of the properties of the employed materials. To ensure maximum cost efficiency, the entire process chain is examined, from the production of the individual components to land transport, preassembly, offshore transport, installation, completion, and operation of the finished structure. The relationships between the predefined design criteria and the developed hybrid substructure are presented in this paper.