Van der Waals heterostructures (vdWHs) represent a novel and largely unexplored class of materials. Since 2013, when Geim and Grigorieva first conceived the stacking of 2D (two-dimensional) materials to create artificial layered structures with tailored properties, a number of promising (opto)electronics devices, e.g. light emitting diodes, solar cells, ultra-fast photodetectors, transistors etc. have been successfully fabricated. It is well established that for isolated 2D semiconductors and vdWHs the optical response is governed by excitonic effects. A theoretical understanding of excitonic effects and of how the electronic screening is affected for the more complex case of multi-layer structures is still lacking due to the computational limitations of standard ab-initio methods.