Water diffusion into composite adhesive joints was experimentally studied by means of gravimetric measurements in bond specimens. The main parameters controlling the diffusion in the bond components were obtained from water uptake experiments carried out in bulk specimens of fiber-reinforced composite and epoxy adhesive. The diffusion of water in bonds is a complex mechanism due to the heterogeneous microstructure of the composite and its interface with the adhesive. This process was simulated through microscale models which represent the microstructure of the composite and of the adhesive joint. Numerical simulations were able to accurately predict the mass gained due to the water uptake and the mechanisms of diffusion through the composite microstructure. These models were employed to evaluate the influence of the geometry and of the material properties on the diffusion of water in a representative composite joint. (C) 2014 Elsevier Ltd. All rights reserved.