One of the great prospects of exascale computing is to simulate chal- lenging highly complex multi-physics scenarios with different length and time scales. A modular approach re-using existing software for the single-physicsmodel parts has great advantages regarding flexibility and software development costs. At the same time, it poses challenges in terms of numerical stability and parallel scalability. The coupling library preCICE provides communication, data mapping, and coupling numerics for surface-coupled multi-physics applications in a highly modular way.We recapitulate the numerical methods but focus particularly on their parallel implementation. The numerical results for an artificial coupling interface showa very small runtime of the coupling compared to typical solver runtimes and a good parallel scalability on a number of cores corresponding to amassively parallel simulation for an actual, coupled simulation. Further results for actual application scenarios from the field of fluid-structure-acoustic interactions are presented in the next chapter.