The interfacial bond parameters are quantified and modeled in this work through experimental and analytical studies. A database comprising 628 shear tests of externally-bonded fiber reinforced polymer (FRP) joints is built for model development. A newly derived closed-form solution is used for identification of bond parameters by matching the analytical solution with test results. Factors that affect the bond parameters are identified and configurations of the models are determined through analytical reasoning. Coefficients of the models are subsequently derived by regression analyses. It is found that the FRP-to-concrete width factor, which has been modeled as a function of FRP-to-concrete width ratio only in all existing bond strength models, should also be a function of concrete strength. A new model for the width factor as a function of both the width ratio and concrete strength is developed, which leads to more accurate and rational bond strength and fracture energy models.