Back-to-back mechanically stabilized earth (MSE) walls are commonly used in the construction of transportation infrastructure facilities. Federal Highway Administration (FHWA) guidelines discuss briefly the design of reinforced back-to-back walls. In this study, a numerical model was developed to study the behavior of connected and unconnected back-to-back walls under working stresses. The effect of reinforcement stiffness on tensile force profiles, the maximum tensile force developed in the reinforcement, and lateral pressures and lateral deformations for both unconnected and connected walls are discussed in detail. A well-defined critical slip surface was observed for the case of the unconnected back-to-back wall with relatively extensible reinforcement. Lateral pressures at the facing in both the cases were found to be almost equal, and the tensile forces developed in the reinforcement for the connected case were found to be uniform along the length of the reinforcement (except at higher depths). © 2020 American Society of Civil Engineers.