This paper deals with the modeling of bistatic scattering from a randomly rough surface. An advanced integral equation model is presented by giving its general framework of model developments, model expressions, and predictions of bistatic scattering for various surface parameters. Extension work to improve the model accuracy is also reported in more detail. In particular, the transition function for the Fresnel reflection coefficient is in more general form. Model predictions are illustrated, demonstrated, and validated by extensive comparisons with numerical simulations. The updated advanced integral equation model remains a compact algebraic form for single scattering and substantially improves prediction accuracy in bistatic scattering that is drawing more emerging applications in earth remote sensing.