One of the key factors affecting the behaviour and reliability of reinforced concrete structures strengthened with externally bonded fibre reinforced polymer (FRP) composites is the bond behaviour between the external composite and the concrete substrate. Extensive research has been carried out on external plate-to-concrete bond strength. This includes experimental studies using various test set-ups, theoretical work using fracture mechanics analysis and finite element analysis and the development of empirical bond strength models. In almost all the theoretical analyses to date, the plane stress assumption has been adopted although the actual stress distribution is likely to be 3D. This paper presents a finite element analysis on the stress distributions in a typical shear test set-up for FRP-to-concrete bond strength. Results show that the stress distribution is significantly different from plane stress assumption primarily because the difference between the width of the test FRP plate and that of the concrete block. It is also shown that the stress distribution is 3D even if the FRP plate has the same width as the concrete block because of the difference of the Poisson's ratio between the constituent materials. (c) 2005 Elsevier Ltd. All rights reserved.