A significant number of studies have been conducted on the shear strengthening of reinforced concrete (RC) beams with externally bonded fibre-reinforced polymer (FRP) reinforcement in the forms of strips, plates or sheets. However, most of these studies have been experimentally based and only a very limited amount of research is available on the numerical modelling of such beams using the finite element (FE) method. The lack of in-depth FE studies is chiefly due to the challenging nature of modelling shear cracking in RC beams and the interfaces between different materials. This paper presents the results of a recent study in which an advanced FE model was employed to investigate the effects of different modelling assumptions for the interfaces between concrete and steel stirrups, between concrete and steel tension bars, and between concrete and FRP on the predicted shear behaviour of RC beams shear-strengthened with FRP. It first outlines the FE model followed by a number of numerical examples to validate it. The effect of varying the bond-slip modelling approach for each interface is then investigated to illustrate its significance. The results presented in this paper show that proper modelling of the bond behaviour of all three types of interfaces is essential in order to accurately simulate the shear behaviour of RC beams shear-strengthened with FRP and that the effects of the assumed bond behaviour of steel stirrups or steel tension bars are very complex and need much further research.