While simulation-based design has become a standard tool in process engineering, most commercial software lacks appropriate membrane process models. Beside the necessity of available membrane data the major obstacle for process design is the lack of a systematic design approach. The latter is especially true for hybrid processes, which despite their complexity provide high potential for process intensification and can facilitate considerable savings in energy, emissions, and capital investment. Thus, an efficient approach for the design of such hybrid processes is highly desirable. Based on a thorough review of the available methods for the design of membrane-assisted distillation processes, we identify current limitations and present a novel optimization-based method for conceptual process design. The formulation of a superstructure in combination with a model decomposition and a stepwise solution strategy facilitates a robust and efficient optimization-based design, which relies on rigorous thermodynamics and bridges the gap between shortcut calculations and a detailed equipment design. The method is demonstrated for three industrially relevant case studies.