The bond between glass fiber-reinforced polymers (GFRPs) and steel reinforcements to concrete is investigated in this study. The experimental program includes two different testing methods (beam tests and pull-out tests) on three different types of reinforcement with various materials, diameters, and surface treatments. For each type of reinforcement rebar and test method, three specimens were tested. A total of 12 beam tests and 12 pull-out tests were performed to analyze the effect of a bar´s diameter, the type of surface treatment, and the configuration of the test on the bond strength of the bar to the concrete. All but one of the bars investigated failed in the pull-out failure mode and showed good bonding behavior to the concrete. The results of the experimental investigation indicate that an increase in the diameter of GFRP bars causes a decrease in the bond stress when a beam bond test is performed and that the surface treatment of GFRP bars has a significant effect on the bond mechanism. Similar bond-slip behavior was observed in both testing methods.