This paper studied the behavior and shear strength of concrete slender beams reinforced with fiber-reinforced polymer (FRP) bars. Nine large-scale reinforced concrete beams without stirrups were constructed and tested to failure. The beams measured 3250 mm long, 250 mm wide, and 400 mm deep and were tested in 4-point bending. Test variables were the reinforcement ratio and modulus of elasticity of the longitudinal reinforcing bars. The test beams included 3 reinforced with glass FRP bars, 3 reinforced with carbon FRP bars, and 3 control beams reinforced with conventional steel bars. Test results were compared with predictions provided by the different available codes, manuals, and design guidelines, indicating that the relatively low modulus of elasticity of FRP bars results in reduced shear strength compared to that of control beams reinforced with steel. The current ACI 440.1R design method offered very conservative predictions, particularly for beams reinforced with glass FRP bars. Based on obtained experimental results, a proposed modification to the current ACI 440.1R design equation is given and verified against test results from other research.