The present paper investigates the different ways humidity may interact with VOCs in building materials. It aims to help in interpreting the results of experiments dealing with the influence of humidity on the reversible sink effect of materials, and/or the VOC emission from walls and furnishings. Three kinds of interactions have been considered: competition for adsorption at the pore surfaces of the materials, as well as change in the diffusion properties and possible absorption / desorption of VOCs due to capillary condensation of water vapour in the micropores of the materials. After briefly presenting the fundamentals of diffusion, capillary condensation, adsorption/desorption and absorption/desorption in porous media, the potential influence of each of these interactions on the VOC transport in building materials has been evaluated for various materials from existing experimental data. The results show that the influence of humidity strongly depends on the porosity and pore size distribution of the materials, as well as the physical properties of the VOCs. Moreover, the VOC mass fluxes at the material surface may vary in a non-linear way with increasing humidity due to changes from one leading interaction phenomenon to another.