Information about the vehicle sideslip angle is crucial for the successful implementation of advanced stability control systems. In production vehicles, sideslip angle is difficult to measure within the desired accuracy level because of high costs and other associated impracticalities. This paper presents a novel framework for estimation of the sideslip angle. The proposed algorithm utilizes an adaptive tire model in conjunction with a model-based observer. The developed algorithm is evaluated through experimental tests on a rear wheel drive vehicle. Detailed experimental results show that the developed system can reliably estimate the vehicle sideslip angle during both steady state and transient maneuvers.